Helicopters in Vietnam

The New Airborne Army

Aviation played a major role in the United States Army  and was organic to most large combat formations rather than organized as a separate branch of the service. During the Vietnam war US Army helicopters, plus a smaller number of fixed-wing aircraft, were used in greater numbers and in more diverse tasks than had ever been seen before in a land war. In fact, US Army aviation had to expand so dramatically that it became, entirely on its own account, the world's third-largest air force.

UH-1 'Slicks' prepare to lift off

Helicopters used by the US Army were generally classified under five main types:

• UH - short for 'Utility Helicopter and used for helicopters that had a primary function as troop transports, command and communication, 'ash-and-trash' missions etc. such as the UH-1 Huey

• AH - this was short for 'Attack Helicopter' and used for those helicopters designed to carry weapons for ground support, and in particular, with reference to the AH-1 Cobra

• OH - this was used for 'Observation Helicopter'. These were helicopters designed to carry out reconnaissance missions such as the OH-6 Cayuse

• CH - short for 'Cargo Helicopter' and covers all helicopters designed primarily as equipment transports such as the CH-47 Chinook

• HH - this was short for 'Heavy Helicopter' but was invariably replaced by the UH or CH classifications.

Sometimes these classifications were changed for a helicopter that was converted to do another task, such as the CH-47 Chinook Gunship which was reclassified ACH-47, 'Armored Cargo Helicopter'. This was not always the case though as with the Huey gunship which retained their original classification, UH-1, rather than becoming AUH-1 or 'Attack Utility Helicopter' for instance.

It was largely because of the Vietnam war that one helicopter in particular, the Bell UH-1 'Huey', became the second most numerous aircraft since World War 2. It provided the backbone not only of US Army air mobility in Vietnam but also, in the later of its many versions, its aerial firepower in the form of 'Hogs' or Gunships. There was no significant clash of arms on the soil of South Vietnam in which the UH-1 did not participate and at the end of the US involvement the number of these helicopters left behind in RVN exceeded the entire helicopter strength of any air force in Western Europe at that time.

Two much larger helicopters were used for heavy lifts. The more common was the Boeing Vertol CH-47 Chinook, a large tandem-rotor transport with a fuselage able to seat 44 equipped troops or carry modest vehicles and artillery. Only the earlier CH-47A and B models were in use in the initial Vietnam conflict, with maximum payload of about 15,000 lb (6804 kg). From September 1968 these were augmented by the CH-47C, with much more powerful engines and a payload of over 23,000 lb (10433 kg) in the voluminous cabin or 28,000 lb (12701 kg) on an external hook. Chinooks could fly in as slung loads all the air-portable guns, ammunition and supply packages used in Vietnam, as well as such mundane items as trucks of drinking water. Chinooks eventually replaced the CH-37 "Mojave" as the primary aircraft recovery helicopter. In this role they are reputed to have picked up and brought back more than 11,000 downed aircraft  - worth a reported $2,990 million - in what were called 'pipe smoke' missions.

Even more powerful, but used in much smaller numbers, the Sikorsky CH-54 'Tarhe" remains the only large crane helicopter in the Western world. Most of the Tarhes in US Army service saw combat duty in Vietnam, carrying as slung loads bulldozers, graders and light armor, picking up and repositioning artillery and also rescuing over 380 downed aircraft.

Among secondary US Army types in Vietnam were small numbers of older helicopters including the Bell OH-13 "Sioux" and OH-23 "Raven" observation helicopters, the Vertol CH-21 "Shawnee" and Sikorsky CH-34 "Choctow" (designated the UH-34 "Dog" by USMC) , and the much newer Bell OH-58A Kiowa. 

Bell UH-1 Series Utility Helicopters

Bell (model 204) XH-40

HU-1

Bell began development of the XH-40 prototype in 1955 to meet an Army specification for a general utility helicopter. First flown on October 20, 1956, the XH-40 was the Army's first turbine powered aircraft. After extensive evaluation, the prototype YH-40, now designated Helicopter Utility YHU-1, was delivered for further testing. Nine HU-1 trainers were delivered in June 1959.

Bell (model 204) UH-1A / UH-1B

The "Huey" as it was called after it's original model designation, the HU-1, was essentially a stretched Bell (model 47) Sioux with room for seven troops or three stretchers in it's cargo compartment behind the pilot. It was redesignated as the Utility Helicopter UH-1 in 1962 under a tri-service agreement. The HU-1A Iroquois, initially procured by the Army in 1959 as a general utility helicopter, was the first model ordered in large numbers. It saw wide use in Vietnam following initial fielding in September 1962. The "Huey" saw service with the 82nd Airborne Division, the 101st Airborne Division, and the 57th Medical Detachment. The "Huey" became the basis for the creation of the 1st Aviation Brigade in 1966.

UH-1A

"Hueys" armed with only two M60D door guns, called "Slicks" because of their uncluttered external appearance, were the backbone of all airmobile combat operations in Vietnam. Unarmed MedEvac "Hueys" were called "Dust Offs", because of the clouds of dust they kicked-up when landing, and were used for the aero medical evacuation of casualties. The "Huey" replaced the CH-21 Shawnee in the combat assault role. The UH-1 had a two-bladed semi-rigid metal main rotor, a two-bladed semi-rigid metal tail rotor and had a speed of 104 mph (90 knots).

The (Bell model 204) UH-1A (1956) seated seven troops. The UH-1A was powered by a Lycoming turbine T53-L-1A 860 shp (shaft horse power) engine. The T53-L-1A was later upgraded to the more powerful T53-L-5 960 shp.

The (Bell model 204B) UH-1B (1960) seated nine troops. The UH-1B featured two long FM homing antennas and the pitot tube on the nose, and a large single window in the doors. The UH-1B was powered by several Lycoming turbine engines; T53-L-5 960 shp, T53L-9A 1100 shp, and T53-L- 11D 1100 shp. The UH-1B had a cruising speed of about 105 mph (90 knots).

Bell UH-1B/UH-1C hybrids

Bell Helicopter proposed upgrading UH-1Bs with the "540" rotor system. This modification was made to about four-to-six UH-1B s in the U. S. The results were promising enough that additional "540" rotor heads were shipped to a very few units in Vietnam. They didn't receive the full UH-1C retrofit: "540" rotor head, new engine, new power train, gears, and rotor shaft, bigger canted tail, bigger tail rotor, asymmetric horizontal stabilizers; just the "540" rotor system.

(1) The first UH-1B/UH-1C hybrid was a plain UH-1B with the "540" rotor head only. It was discovered that in Vietnam's "hot and high" flying environment, their performance was marginal, and they could exceed the tail rotor torque limits. Also, they were too heavy for the UH-1B's T53-L-5 960 hp engine.

(2) The second type of hybrid was the UH-1B with the "540" rotor, T53-L-11D 1100 hp engine upgrade, power train, and tail rotor. These modifications improved performance, but with the increased torque from the more powerful engine, and larger tail rotor, the tail had to be modified by adding the camber and increasing the width. These modifications were incorporated into what became the UH-1C model. One unit which flew UH-1 B/UH-1C hybrids was the 174th Helicopter Assault Company.

The Bell UH-1C (1965) could seat nine troops, had the improved rotor and had a greater range. The UH-1C was powered by a single Lycoming T53-L-11D 1100 shp engine. The rotor head was the "540" rotor system, used only on the UH-1C (and the UH-1M). This was the prototype of the rotor system later used, without stabilizer bar and dampers, on the AH-1G Cobra. The chord of the rotor blades (distance from the leading edge to the trailing edge) was much wider on the UH-1C than on all other model "Hueys". The UH-1C also featured a brace extending from the aft fuselage to the weapons mount. This support was only used on the UH-1C and the UH-1M, an engine upgrade to the UH-1C. These aircraft were also the only "Hueys" with the fuel filler cap located on the left side of the fuselage.

The UH-1M was a small number of UH-1C models that were upgraded to the more powerful Lycoming T53-L-13B 1400 shp engine for use in Vietnam. The first three UH-1Ms were equipped with the INFANT (Iroquois Night Fighter and Night Tracker) system for night operations. All remaining UH-1Ms were simply UH-1Cs with the T53-L13B engine upgrade.

It must be noted that UH-1's were also used in considerable numbers by the US Air Force, Marines and Navy in Vietnam, the two latter services employing these helicopters in a all kinds of armed assault and rescue missions as well as for patrolling the vast Mekong Delta region. But the US Army used the Huey in greater numbers than any other Branch of Service, mainly as the standard transport of the Air Cavalry, which were the basic airborne assault units ready to be sent anywhere they were needed. Of equal importance was the use of the UH-1 in the devastating role of aerial rocket artillery (ARA). If there was a weakness in the overall mission it was that the US Army did not really hold the territory, except locally, and particularly not at night; airborne assaults were on specific objectives either to capture particular ground features or, usually, to engage an identified hostile ground force and destroy it or cause it to retreat or disperse. Invariably it meant landing ground forces, including artillery and all the immediately needed supplies, in the face of close-range enemy fire. Skill and courage had to be backed up by progressive improvements in the helicopters to enable them to survive large numbers of small-arms strikes and even occasional hits by calibers up to 23mm as well as shell splinters, blade impacts with treetops and exceptionally heavy landings.

In each airmobile operation at least one UH-1 would be specially equipped with communications systems and would carry the force commander and other specialist personnel, including an air liaison officer whose task was to direct any close air support, TACAIR, by USAF, USN and USMC aircraft. In a major operation an air liaison officer team might number as many as five FAC pilots and eight communications specialists, with frequencies covering all ground and air (and, if involved, sea) forces in the area. Another UH-1, the leading aircraft in the formation, would carry the LZ (landing zone) control party, tasked with alighting on the LZ ahead of all other helicopters and guiding the latter in.

Selection of a suitable LZ depended on prior close helicopter reconnaissance of the area. Occasionally no LZ was available, and troops had to be put down (by abseiling down ropes if necessary) from machines at the hover. This might be necessitated by lack of firm soil, or absence of sufficient reasonably level ground. Where there was dense cover by tall trees an instant LZ would be created by exploding a gigantic bomb fused to detonate well above ground level, thus sweeping trees flat over a large radius without making a crater. Bombs of up to 15,000 lb (6804 kg) were used.

Once the operation was mounted there was little time to do any preparation at the LZ, and the LZ control party's job included warning helicopter pilots (who were mainly young enlistees given the rank of warrant officer on gaining their wings) of hazards in the LZ, location of ground fire and anything not going according to plan. The objective was to get each Huey back in the air after a ground time of less than ten seconds, and five if possible.

Throughout the operation the closest offensive support would be provided by a so-called Pink Team made up of one or more pairs of fast agile helicopters. One of the pair would be a 'Loach', a Hughes OH-6A Cayuse (named from its original designation of LOH, light observation helicopter). Extremely small and maneuverable, the OH-6A often carried weapon systems such as Minigun or XM27 packs or an XM75 grenade-launcher, but its main role was to carry a crew of from two to four as close as possible to any place in the LZ locality where enemy forces might be waiting. It was a highly dangerous job; one Loach pilot was collected by rescue aircraft six times after having been shot down by point-blank fire. Everything discovered by Pink Team observers was immediately radioed to the LZ and to the force commander.

Doing its best to protect the Loach and the other members of the Pink Team, the Bell AH-1 Huey Cobra was quickly developed by Bell Helicopter to replace the cancelled AH-56A, the planned USA armed helicopter gunship bristling with sensors as well as armament. The Huey Cobra was somewhat smaller and simpler, and after quick development got into action in Vietnam in autumn 1967, for the first time bringing heavy firepower into the USA airmobile companies. Slim, agile and well-protected, even the first versions of Cobra carried devastating firepower from machine-guns, cannon, grenade-launchers and up to 76 high-velocity rockets. Subsequently, additional weapons were able to be fitted, as well as sensors such as the nose-mounted Smash (SE Asia Multi-sensor Armament System for Huey Cobra) with IR (infra-red) and MTI (moving-target indication) radar automatically linked to the weapon aiming subsystems. Cobras made a considerable difference to airmobile operations in bringing heavy suppressive fire to bear within seconds; they not only made the defenders keep their heads down, but often eliminated them.

A few of the helicopters normally used only for transport were equipped with special sensing devices, all of them designed specifically to solve problems created by the Vietnam environment. Night observation devices were numerous, most of them using IR (infra-red) or passive image-intensifying electronics in order not to give away the exact position of the aircraft carrying it. Several CH-47 Chinooks were equipped with radar and other sensing and night-vision devices, as well as three ACH-47 attack conversions with heavy and diverse armament installed as part of the helicopter, in addition to five extra guns aimed by air gunners from positions along the side of the cabin.

One of the most unusual sensors was a so-called People Sniffer, flown in Vietnam on several UH-1 Hueys. The system, comprising the sole payload of the helicopter, continuously analyzed the atmosphere drawn through instrumentation tubes and recorded the presence of chemicals for example, found in perspiration and exhaled breath-indicative of human activity. The difficulties were that such chemical emissions are present in only a few parts per billion, and so did not Positively mean hostile troops were present but merely suggested humans somewhere upwind of the helicopter, and the unmistakable noise of the helicopter gave several minutes' warning of its approach.

Hospitalization and Evacuation

The peculiar nature of counterinsurgency operations in Vietnam required modification of the usual concepts of hospital usage in a combat area. There was no "front" in the tradition of World War II. The Amy checkered the countryside with base camps. Although any one of these might become a battlefield, the base camp was relatively secure unless it was under attack. Semi-permanent, air-conditioned, fully equipped hospitals were constructed at a number of these camps. In contrast to World War II and the Korean War, the hospital did not follow the advancing army in direct support of tactical operations. All Army hospitals in Vietnam, including the MUST (Medical Unit, Self-contained, Transportable) units, were fixed installations with area support missions. Since there was no secure road network in the combat area of Vietnam, surface evacuation of the wounded was almost impossible. Use of the five separate companies and five detachments of ground ambulances sent to Vietnam was limited largely to such functions at base camps as transportation between the landing strip and the hospital or the routine transfer of patients between neighboring hospitals when roads were secure. Air evacuation of the injured became routine.

Getting the casualty and the physician together as soon as possible is the keystone of the practice of combat medicine. The helicopter achieved this goal as never before. Of equal importance was that the Medical Department was getting the two together in a hospital environment equipped to meet almost any situation. The degree of sophistication of medical equipment and facilities everywhere in Vietnam permitted Army physicians to make full use of their training and capability. As a result, the care that was available in Army hospitals in Vietnam was far better than any that had ever been generally available for combat support. The technical development of the helicopter ambulance, a primitive version of which had been used to a limited extent in the Korean War, the growth of a solid body of doctrine on air evacuation procedures, and the skill, ingenuity, and courage of the aircraft crewmen and medical aidmen who put theory into practice in a hostile and dangerous environment, made possible the hospitalization and evacuation system that evolved in Vietnam. The system worked effectively because it was compatible with the characteristics of warfare in that country.

In-Country Evacuation

Highly mobile and widely deployed forces must have a highly mobile and flexible medical evacuation system immediately responsive to their needs. The helicopter ambulance provided this flexibility and responsiveness in Vietnam. At the peak of combat operations in 1968, aero medical support was provided by 116 air ambulances. These helicopters could transport six to nine patients at a time, depending upon the number of litter cases. Medical evacuation flights averaged only about 35 minutes each, a feat which often meant the difference between life and death for hundreds of patients. The more seriously wounded usually reached a hospital within 1 to 2 hours after they were injured. Of the wounded who reached medical facilities, about 97.5 percent survived.

The helicopter brought modern medical capabilities closer to the frontline than ever before. Furthermore, combined with a medical radio network, the helicopter provided greater flexibility in regulating patients. Preliminary evaluation of the injury and the condition of the patient was made while in flight, and the use of the radio network permitted redirecting the patient to the nearest hospital suited to his needs. If a hospital developed a surgical backlog, the combination of helicopter and radio facilitated regulating patients according to available operating facilities, rather than available beds. This combination was the core of the Army medical management system in Vietnam.

The Buildup of Air Ambulance units

The buildup of air ambulance units paralleled the commitment of U.S. combat forces to Vietnam. The first air ambulance unit sent to Vietnam, the 57th Medical Detachment (Helicopter Ambulance), later nicknamed "The Originals", arrived in 1962 to support the 8th Field Hospital at Nha Trang. The unit was authorized five UH-1A aircraft, which were replaced by an improved model, the "B" version, in March 1963. Initially, two aircraft were stationed at Qui Nhon and three in Nha Trang. As fighting increased around Saigon and in the Delta, the helicopters were shifted from place to place in response. The 82d Medical Detachment (Helicopter Ambulance) became operational in IV CTZ (the Delta), in November 1964.

The buildup of units continued at an accelerated pace in 1965. The 283d Medical Detachment (Air Ambulance) arrived in August 1965, followed by the 498th Medical Company (Air Ambulance) in September. The 254th Medical Detachment (Air Ambulance) arrived in Vietnam before the end of the year but did not become operational until February 1966 because a backlog at the port delayed the arrival of the unit's equipment. The four detachments, each authorized six helicopters under a new table of organization and equipment, supported III and IV CTZ's. The 498th Medical Company, which was authorized 25 aircraft, supported II CTZ.

During 1967, the 45th Medical Company (Air Ambulance) and four additional air ambulance detachments arrived in Vietnam. The units were shifted from location to location to provide the most effective area coverage in response to tactical operations. In 1968, four additional detachments were sent to Vietnam, completing the buildup of aero medical evacuation units. One unit, the 50th Medical Detachment, which was assigned to the 101st Airborne Division in mid-1968, became the nucleus of the division's air ambulance platoon. By 1969, there were 116 field-army level helicopter ambulances in Vietnam. These were assigned to two companies and 11 separate detachments. (Map 1)

Air Force Aero medical Evacuation Support

The Army and the U.S. Air Force evacuation systems complemented each other, each carefully continuing the movement of wounded or sick until they reached a final-destination medical facility.

Based on experience gained in World War II and the Korean War, the U.S. Air Force initially used returning assault or cargo aircraft for casualty evacuation. The system worked well during the early stages of the Vietnam War because the number of sick and wounded was relatively low. As troop strength increased and combat operations became more intense, the system grew progressively less satisfactory. The requirements for evacuation often coincided with the most urgent needs for resupply, although not always at the same location.

Map 1

The old system was therefore abandoned in favor of a new one in which aircraft were regularly used specifically for evacuation purposes. The 903d Aero medical Evacuation Squadron scheduled the first regular in-country evacuation flights in 1967. By late 1969, the number of regular scheduled flights had increased to 188. The assault aircraft initially used for aero medical evacuation were supplemented, in early 1968, by C-118 cargo aircraft specifically modified for evacuation missions. The average number of patients moved increased from 5,813 per month between July 1967 and January 1968, to 9,098 from March to June 1968. During the Tet Offensive in February 1968, more than 10,000 patients were evacuated by the Air Force.

"Dust-off"

Those Army medical evacuation helicopter units not organic to divisions came to be called Dust-off, after the radio call sign of the most famous of the early pilots, Major Charles L. Kelly, MSC, who was killed in action on 1 July 1964. Several scores of these flying "medics" flew their unarmed helicopters into hostile areas, risking their own lives to save those of others. In a 2-year period, 39 crew members were killed and 210 wounded in aero medical evacuation missions.

The combination of the helicopter ambulance and a medical radio network was the basis of the effective medical regulating system that evolved in Vietnam. During the first phase of U.S. troop commitment to Vietnam in early 1965, there was only one hospital in support of each CTZ and therefore no alternative to the destination of a casualty. As the number of hospitals and the number of casualties increased however, the need for a regulating system became imperative. The first system in the III and IV CTZ's was set up with Air Force Radar Tan Son Nhut, Paris control. Dust-off helicopters inbound called Paris control which had a direct-line field telephone, "hot line", to the MRO (medical regulating office) and the 3d Field Hospital. The three major treatment facilities available were the 3d Field Hospital, the 93d Evacuation Hospital, and the 3d Surgical Hospital, the last named then located at Bien Hoa. The MRO confirmed or changed the destination chosen by the pilot as the medical situation indicated.

After Headquarters 44th Medical Brigade arrived in Vietnam in 1966, the brigade MRO became responsible for all in-country regulating of patients. Medical groups controlled the movement of patients from tactical areas to hospitals within their own group areas. Further movement of patients from one group area to another was coordinated by medical group MRO's with the brigade MRO, who maintained over-all control, to insure proper usage of all medical facilities.

Telephone communications were abysmally poor and radio communications not much better during this period. When heavy fighting produced a large number of casualties and medical regulating was most urgently needed, operational radio traffic was also heaviest. Moreover, since short-range radios were used, requests for evacuation had to be routed from divisional medical battalions to backup hospitals by way of the Dust-off radio network or through the supporting field army medical group. This cumbersome method caused delays and sometimes resulted in garbled transmissions.

On an experimental basis, the 55th Medical Group at Qui Nhon borrowed single-sideband long-range radios from the 498th Medical Company (Air Ambulance). Originally placed in the air ambulance company for long-range transmissions to its aircraft on evacuation missions, these radios had been little used because of the relatively short distance of most flights and the extensive maintenance they required. Their use for medical regulating proved highly successful, and an additional 54 sets were ultimately acquired to expand the communications network throughout the medical brigade.

Medical regulating started on the battlefield. Medical groups placed regulators (senior noncommissioned officers) in areas of troop concentration or at the site of a combat operation. In co-operation with the local medical unit, the regulator radioed requests for evacuation to the supporting Dust-off unit. The transmission was monitored by the MRO at his medical group headquarters.

In the absence of a field medical regulator, a request for air evacuation was normally made by the medical aidman at the site of the casualty. The request, which included such information as the number of patients by type, the exact location by map grid co-ordinates, data on enemy movements, and the radio frequency of the requesting unit, was transmitted over the Dust-off radio network to the supporting air ambulance unit. Frequently the call was received by an air ambulance already in flight which could be diverted from a less urgent mission. If not, a standby crew at a field site or at the unit headquarters, scrambled to make the pickup.

After proper identification of the ground force with the casualty, the Dust-off helicopter generally made a high-speed or tight-circle approach into the area. Time spent on the ground in a normal operation was usually between 30 seconds and 1 minute, depending on the number of casualties. The casualty was given emergency treatment by the medical aidman on board as soon as the aircraft was out of the combat area.

The patient was flown directly to the medical treatment facility best able to give the care required. This might or might not be the one nearest the site of injury. The decision as to the proper destination hospital was based on several factors. Distance was less important than time; the objective was to reduce the time between injury and definitive treatment to the minimum. Information based on the preliminary in-flight evaluation of the injury and the condition of the patient, knowledge of existing surgical backlogs, and the over-all casualty situation were other considerations. If the aircraft commander questioned the destination selected by the medical regulator because of his knowledge of the patient's condition, a physician was consulted by radio while the patient was still in transit before the decision became final. The inbound medical aircraft commander informed the receiving hospital by radio of his estimated time of arrival, the nature of the casualties on board, and any special reception arrangements that might be required. Thus, the receiving hospital was able to have everything in order to receive casualties and begin definitive surgical care.

Helicopter evacuation techniques and requirements varied by geographic area, type of combat operation, and type of equipment available, and changed from year to year as experience modified and refined procedures. Since the air ambulance was unarmed, gunship support was requested if the ground reported contact with the enemy in the vicinity of the pickup site, or if the rescue was a hoist operation.

In "hot" areas, the crew of the evacuation aircraft consisted of a pilot, copilot, crew chief, medical aidman, and a man armed with an automatic rifle. In quieter areas, the rifleman was left behind in favor of increased patient capacity. On hoist operations in mountainous and jungle, terrain, before the more powerful "H" model aircraft was introduced, the crew consisted only of a pilot, copilot, and hoist operator. On these missions, fuel load was also generally reduced in favor of greater lift capability. Night missions were quite common, often comprising 15 to 20 percent of the total missions in some areas.

Helicopter rescue operations were aided by new equipment designed especially for use in jungle terrain or in combat areas where it was too dangerous for a helicopter to land. The hoist consisted of a winch and cable on a boom which was moved out from the aircraft when it arrived over the rescue site. At the end of the cable was a ring and hook to which a Stokes litter, rigid litter, or forest penetrator could be attached. The cable could be lowered at the rate of 150 feet per minute and retracted at the rate of 120 feet per minute. The forest penetrator, a spring-loaded device which could penetrate dense foliage, opened to provide seats on which a casualty could be strapped. It was preferred over the litter by the crews for hoist rescues because it was less likely to become entangled in the trees.

Hoist operations significantly increased the danger for Dust-off crews. Hovering above the jungle or a mountain side as it lowered its cable, the helicopter became a "sitting duck" for enemy troops in the area. In 1968, 35 aircraft were hit by hostile fire while on hoist missions. The number increased to 39 in 1969. Nonetheless, the hoist was used extensively and to great advantage in Vietnam. Its use permitted the rescue of 1,735 casualties in 1968 and 2,516 casualties in 1969, who otherwise could not have been retrieved.

The primary mission of the Army helicopter ambulance was the in-country aero medical evacuation of patients. The number of patients evacuated by aero medical evacuation helicopters rose from 13,004 in 1965, to 67,910 in 1966, to 85,804 in 1967, and peaked at 206,229 in 1969. These figures included members of the ARVN, Vietnamese civilians, and Free World forces as well as U.S. patients. Each time a patient was moved by helicopter, the move was entered in the tally. Thus, if a patient was taken to a surgical hospital by helicopter and later transported from there to an evacuation hospital by helicopter, this would count as two patients evacuated. Army air ambulances completed more than 104,112 aero medical evacuation missions while flying approximately 78,652 combat hours in 1969.

In addition to this primary mission, Army helicopters were also used to transport professional personnel, medical supplies, and blood to medical facilities. Supplemented by scheduled Air Force flights, and from time to time by larger helicopters, they were also used to transport patients between hospitals for consultations or to free beds in areas where increased casualties were anticipated.

CH-21 Shawnee Assault Helicopter

AH-1G Cobra Attack Helicopter

(2) Bell made use of existing technology by designing a streamlined fuselage using the same Lycoming T53-L-11 1100 shp engine, drive train, gear boxes, rotor system, boom and tail unit from the model UH-1C "Huey". The "540" rotor system, developed for the UH-1C was modified by development of a computerized stability control augmentation system (SCAS) for use in place of the short weighted gyro-stabilizer bar first used on the Bell (model 47) OH-13 Sioux.

AH-1G of the 1st Cavalry Division (Airmobile)

Some early model AH-1G Cobras mounted either two M134 "Miniguns" or two M129 grenade launchers in a M28A1 chin-turret (TAT-141). Because of problems with the ammunition feed systems, the twin-gun configuration was discontinued. The Cobra was first employed to Vietnam with the 1st Cavalry Division (Airmobile) in August 1967. The Cobra's primary mission was to give fire support to troop carrying "Hueys". The AH-1G Cobra was powered by a single Lycoming T53-L-13 1400 shp turbine engine, and had a speed of 196 mph (170 knots), almost twice the speed of the UH-1 "Huey". The AH-1G Cobra used the M73 reflex sight. The Cobra performed it's job so well it was possible for the first time for "slicks" and gun ships to operated as true air cavalry.

Later models of the AH-1G Cobra, or "Snake", were armed with 2.75 inch (70mm) Folding Fin Aerial Rockets (FFARS) in M158 seven-tube or M200 19-tube rocket launchers, used so effectively at An Loc in 1972. The Cobra had a chin-turret on the M28/M28A1 armament subsystem. The chin-turret mounted the M134 7.62mm "Minigun" and the M129 40mm grenade launcher. The AH-1G could also be armed with the M134 "Minigun" in fixed side-mounting M18/M18A1 gun pod, and the port (left) side mounting M195 20mm automatic gun on the M35 armament subsystem. The AH-1G could also mount the XM118 smoke grenade dispenser.

M195 six-barrel 20mm automatic gun on M35 fixed mount armament subsystem	Inboard M195 six-barrel 20mm automatic gun  and outboard M158 seven-tube 2.75 inch rocket launcher

The Bell (model 209) AH-1G Cobra featured the new "540" wide-bladed rotor and a slim fuselage that gave it twice the speed of the UH-1B "Huey". It could loiter over the target area three times as long, and had an improved armament system over previous gun ships. Tandem seating of the two crew members in the Cobra, with a width of just 38-inches, presented a much smaller target than the 100-inch wide UH-1 "Huey". The Cobra had a two-bladed semi-rigid seesaw bonded all metal main rotor and two-bladed rigid delta hinge bonded all metal tail rotor. The AH-1G Cobra's mission was direct aerial fire support, armed escort, and reconnaissance.

Bob Shlikas wrote;

I was searching for models of the AH-1G when I found your site.  I'm writing because of the questions you raised on rocket pod configurations for the Cobra.  From February 1969 until September 1970, I was a helicopter pilot assigned to the 25th Aviation Battalion, 25th Infantry Division in Cu Chi, Vietnam.  While there, I flew first for A Company, a slick company, and then for B Company, a General Support or gunship company.  During that extended tour, I flew primarily UH-1C gunships and Cobras.  I also spent lesser amounts of time in UH-1D, UH-1H, and OH-6 helicopters.

But back to the rocket pods.  At that time there was no standard configuration or set of configurations. Armament was chosen to suit the mission and the fire team leader's desires.  With two turret stations and four wing hard points, the combinations possible were extensive.  Options in the turret were the 7.62 mini-gun or the 40mm grenade launcher in any combination.  The wing hard points gave us the option of 7.62 mini-guns, 7 shot rocket pods, 19 shot rocket pods, or a 20mm mini-gun.  The 7 shot and 19 shot pod combination that you built was extremely common.  When we used that combination of rocket pods, we put the larger pods on the inboard hard points, but I know of no reason that the combination you used should not be possible. My personal favorite configuration, since we shot primarily in support of ground troops in contact with the enemy, was 4 of the 19 shot pods with 2 grenade launchers in the turret.

The most critical limitation to choice of armament was the weight of the aircraft.  We were constantly battling degradation of performance due to consistently operating at high temperatures.  The high turbine inlet air temperature reduced the turbine output, while the high ambient also caused a reduction in rotor efficiency.  Dusty or dirty rotor blades worsened the problem.  We had to be very conscious of our fuel loads in order to maintain the ability of the aircraft to hover.  The UH-1 gunships were the worst offenders in this regard.  A large percentage of UH-1C departures required sliding or bouncing to get the aircraft through translational lift and actually flying. I hoped this helped with your armament questions.  If there is anything else that I can offer, please e-mail me.  Your models are impressive.  Keep up the good work.

Early AH-1G Cobra Night Vision Systems. The AH-1G was equipped with the CONFICS (Cobra Night Fire Control System) and the SMASH (Southeast Asia Multi-Sensor Armament Subsystem for "Huey" Cobra) systems to provide the Cobra with the capability of detecting, identifying, and targeting ground targets during day or night operations.

OH-13 Sioux Light Observation Helicopter

The Bell (model 47) H-13 Sioux, with a crew of three, was one of the most popular light utility helicopters ever built. The Bell model 47 was produced continuously from 1946 to 1973. The U. S. Army Air Force procured it's first YR-13 (model 47B) in December 1946. The OH-13 had a cruising speed of 70 mph (60 knots).

The OH-13 Sioux also saw service during the early days of the Vietnam war before the fielding of the OH-6A Cayuse in early 1968. The Sioux had a single, two-bladed main rotor and a metal two-bladed tail rotor. The H-13 had a speed of 106 mph (92 knots). The Sioux could be armed with twin M37C .30 Cal. machine guns on the XM1 armament subsystem or twin M60C 7.62mm machine guns on the M2 armament subsystem.

The XH-13F, powered by a Continental-Turbomeca XT51 Artouste I 220 hp turbo shaft engine, was Bell Helicopter's first turbine powered aircraft.

Bell (model 47) power plants were:

An experimental armed Bell (model 207) Sioux Scout (1963), based on the a Bell (model 47G-3B 1) body and engine, with a newly developed gun ship front end, aided in the development of the AH- I G "Huey" Cobra attack helicopter.

The Army's enduring relationship with the Bell Model 47 light helicopter began in December 1946, when the USAAF procured a single example for operational evaluation by the Army ground forces. This essentially standard commercial Model 47A was designated YR-13, and was soon followed into service by seventeen identical aircraft. The YR-13 was powered by a single 175 hp Franklin 0-335-1 piston engine, offered accommodation for a pilot and one passenger, and featured wheeled landing gear and a fabric-covered tail boom. The R-13's performance was judged to be exceptional, and the type subsequently became the first helicopter produced on a large-scale to enter Army service following the 1947 Army-USAF split. Between 1946 and 1970 the Army procured a total of 2197 Sioux of the following variants:

YR-13A: Three standard YR-13 machines (serials 46-228 to -230) of the first evaluation batch modified for cold weather trials in Alaska in early 1947. The 'winterizing' process included the installation of improved cabin heaters, cabin insulation, some additional instrumentation, and minor modifications to the engine, transmission, and dynamic components. In 1948 all three aircraft were redesignated YH-1 3A in accordance with the services' joint adoption of the H-for-helicopter designation prefix.

One of the Army's two H-13K research machines hovers
above its Fort Rucker pad in late 1961.

H-13B: Designation allocated to the sixty-five production aircraft (48796 to -860) procured by the Army in 1948. This version was derived from the commercial Model 47D and was powered by a 200 hp Franklin 0-335-3 engine, had the now-distinctive plastic 'bubble' canopy, and incorporated minor detail changes. All but two of these aircraft were delivered prior to the outbreak of the Korean War, and many examples of this and other variants ultimately participated in that conflict.

YH-13C: Designation given to a single H-13B withdrawn from normal service in 1950 for use as an engineering testbed. The machine was fitted with the now-familiar metal skid-type landing gear in place of the then-usual wheeled undercarriage, its rear fuselage covering was removed, and it was experimentally fitted with various types of external stretcher-carrying devices for evaluation in the casualty evacuation role.

H-13C: A total of sixteen H-13B aircraft modified in 1952 for service as air ambulances. These helicopters incorporated the skid landing gear and open-lattice tail boom of the YH-13C, and were capable of carrying two stretchers on external racks fitted to the tops of the skids.

H-13D: This variant was based on the commercial Model 47D-1, and was powered by the 220 hp Franklin 0-335-5 engine. The aircraft was outwardly similar to the H-13C, with the open-lattice tail boom, skid landing gear, and external stretcher attachment points, though not all of the eighty-seven examples procured (51-2446 through -2531, and 51-16642) were used in the air ambulance role. Those examples remaining in the Army inventory in 1962 were redesignated OH-13D.

H-13E: Designation given to 490 production aircraft (51-13742 to -14231) essentially identical to the H-13D but with dual flight controls and a third seat. Redesignated OH-13E in 1962.

XH-13F: In 1955 a single H-13D was experimentally fitted with a 240 shp Continental (Turbomeca) XT51-T-3 shaft turbine engine. This modification was not adopted for operational use and the aircraft was eventually returned to H-13D standard.

H-13G: In 1953 Bell introduced the improved commercial Model 47G, which featured a small mounted-mounted elevator for improved stability, greater internal fuel tankage, dual flight controls, and accommodation for a third person. The Army took delivery of the first of 265 examples in 1954. Those remaining in service in 1962 were redesignated OH-13G.

H-13H: This variant was based on the commercial Model 47G-2 and had an updated 250 hp Lycoming VO-435 piston engine, all-metal rotor blades, dual flight controls, and external stretcher attachment points. The Army acquired at least 453 examples of this variant beginning in 1956. Redesignated OH-13H in 1962.

H-13K: Designation given to two production H-13H machines modified to commercial Model 47G-3 standard through the installation of 225 hp Franklin 6VS-0-335 engines, longer rotor blades, and other detail changes. These helicopters were optimized for high altitude operation and were evaluated at Fort Rucker, Alabama, in 1960 and 1961. Both were redesignated OH-13K in 1962.

Though modified for high altitude flight these aircraft retained the pod and open lattice boom layout, bubble canopy, streamlined fuel tanks, and simple skid landing gear that characterized the entire H-13 series. Both H-13Ks were redesignated OH-13K in 1962.

OH-13S: In 1963 the Army accepted the first of an eventual 265 examples of this variant, which was derived from the commercial Model 47G-3B. The OH-13S was some sixteen inches longer than the standard -H model Sioux and was powered by a turbo-supercharged 260 hp TVO-435-25 piston engine. The OH-13S could accommodate two persons in addition to the pilot, and had a gross weight of 2855 pounds.

TH-13T: Designation allocated to the last H-13 variant acquired by the Army, a dual-control instrument flight trainer. A total of 411 examples was delivered beginning in 1963. Generally similar to the commercial Model 47G-3B-2, the TH-13T was powered by a 270 hp Lycoming TVO-435-D1 B engine and accommodated one student in addition to the instructor pilot.

OH-6A Cayuse Light Observation Helicopter

Light Observation Helicopter (LOH) program (1960-1968)

In 1960, the U. S. Army requested proposals for the LOH program, a small, maneuverable, personnel transport, cargo, MedEvac, light ground attack, artillery, and photo reconnaissance helicopter. The LOH program was won by the Hughes (model 369) YOH-6A Cayuse. Though not selected, the Bell (model 206) YOH-4A (1961), powered by an Allison T63-A-5 250 shp turbine engine, evolved into the successful Bell (model 206A) Jet Ranger. When the LOH program was reopened for an additional buy in March 1968, the Army selected the Bell model 206A, which was type classified as the OH-58A Kiowa light observation helicopter.

The Boeing (McDonnell Douglas - formerly Hughes model 369A) OH-6A was designed for use as a military scout during the Vietnam war to meet the U. S. Army's need for an extremely maneuverable light observation helicopter (LOH). Initially fielded in Vietnam in early 1968, the Hughes OH-6A was used for command and control, observation, target acquisition, and reconnaissance. The Cayuse was organic to division, brigade, and battalion size units. The four-passenger tear-drop shaped "Flying egg" (six-passengers with rear seats folded down) was a small, light, sturdy, maneuverable helicopter, with very low drag.

The OH-6A Cayuse was quite effective when teamed with the AH-1G Cobra attack helicopter as part of what were known as "Pink Teams". The OH-6A "Loach" (for "LOH") would find targets by flying low, "trolling for fire", then marking the target with colored smoke to lead in a Cobra, or "Snake", to attack. The Cayuse could absorb an extensive amount of small arms fire and still bring the crew home safely. The OH-6A could be armed with the M27 armament subsystem, the port (left) side mounting M134 six-barrel 7.62mm "Minigun" or a 40mm grenade launcher on the XM8 armament subsystem. In addition, an M60D 7.62mm machine gun could be mounted in the rear starboard (right) door opening. The OH-6A replaced the Korean era OH-13 Sioux and OH-23 Raven light observation helicopters. The Cayuse had a single articulated four-bladed main rotor, a metal two-bladed tail rotor, and a V-shaped tail. The OH-6A was powered by a single Allison T63-A-5A 285 shp turbo shaft engine, and had a cruising speed of 144 mph (125 knots).

"The Real Cav OH-6G"

The "OH-6G" was the creation of the Maintenance Section of "The Real Cav", B Troop 7/17th Air Cavalry Squadron, which was stationed near Pleiku in early 1972. Armed with a 40mm grenade launcher in a nose turret, and two 19-tube 2.75 inch rocket launchers, the "OH-6G" was ready to take on anything. Unfortunately, the weight of the armament kept the little bird from taking off.

Bill Walton and the OH-6G

Bill C. Walton, former B Troop Maintenance Officer, wrote;

The OH6G was created by the Maintenance Section of B Troop 7/17 Air Cav (The Real Cav) in 1968, while we were at Camp Enari, near Pleiku. I didn't find a picture of it on you website so thought I would send it to you. I am in front of the aircraft, which, although it couldn't hover/fly, did look "mean"

Here is the story as to how it came to be.

I was the Aircraft Maintenance Officer of B Troop, 7/17th Air Cavalry Sqdn, in 1967-68. We were equipped with UH-1Cs, UH-1Hs and OH-6As and were located in Camp Enari, near Pleiku. One day, in 1968, we were a little "short" on mission ready UH-1Cs so my Maintenance section decided to "modify" an OH-6A.

With the assistance of Armament Specialist Anthony Holmes, I hung rocket pods on angle irons that were laid in the floor and stuck out of both sides of the aircraft. Then we hung an empty 40mm grenade launcher turret on the front of the bubble using safety wire. The tube sticking out of the turret was a rolled up file folder which Holmes painted black using shoe polish. We called it "our OH6G" (Gunship) and I invited all the Scout pilots to come, look, and fly if they wanted to. Of course all they could do was look and take pictures. After the photo session, we removed the weapons system and it was an OH6A again.

This picture somehow made it to the Army Aviation School, at Ft Rucker Alabama, and was copied and used so many times (in pre email/digital days) that it had became almost a line drawing. The last time I saw it at the Avn School was the winter of 1970. A few years ago Hughes aircraft discovered the OH-6G picture and wanted to use it. I agreed but told them there was a major problem with the original slide as, apparently, the processing chemicals in the Pleiku PX were too hot/whatever and there were minor cracks in the emulsion (which are readily seen). They told me that they could fix it, so I mailed the slide to them, but they returned it with the remark that the cracks in the emulsion were more than they could handle. I would imagine that someone who knows what they are doing could eliminate the cracks/lines in the picture using Photoshop or some other computer program. But that is beyond my computer capabilities.

B Troop, 7/17th was the 1st Unit to take OH-6As to Vietnam, according to the Army Aviation Heritage Foundation (AAHF). I am not really sure how this conclusion was arrived at since the 7/17th Air Cav Squadron all arrived in Vietnam at the same time. Possibly there is a connection between the facts that one of the AAHF officials, Glen Carr, was a former B Troop Commander, but someone else will need to figure that out.

Whilst the Maintenance Section's heavily modified 'OH-6G' may have been one modification too many, successful field modifications were adopted.

Rich Hefferman (B Troop, 7/17th Air Cav 'Ruthless Riders') wrote;

For what its worth in June of '68 I crewed a LOH  67915 that carried both the M127 mini-gun and a 4 shot 2.75" rocket pod. This was not the field modified 2-shot pods that some units fielded. We did trade off some power especially because of the air working the Central Highlands.  By using a two man crew and using a CAR-15 instead of a third crewman using an M60 we broke about even on the gross weight. I have several photo's of the ship posted at the link above under the "Scout's 68-69" heading.

Rich Hefferman's aircraft with the modified armament system. Notice the rocket pod on the right pylon. (Photos courtesy of Rich Hefferman)

In June of '68 B Troop 7/17th Air Cav modified aircraft 67915 to utilize both the M-27 mini-gun and a 4 shot 2.75mm rocket pod. The armorer who worked on the ship was Tony "Limey" Holmes and the Loach was crewed by myself. The rockets used, to the best of my recollection, were always W-P (white phosphorous) which were used to mark targets for our UH1-B Model gunships until we received our AH1-G Cobra's. The system did work well. The problem was that while you were scouting the area if you received fire you had to mark the target immediately with smoke to bring accurate gunship fire on the target. This was not possible unless you fired the rockets from a distance to mark the target. Although it must have shocked the NVA to see an OH6 roll in hot firing both a mini-gun and punching off rockets at the same time. At the time B Troop used a two man crew with the CE/Obs using a CAR 15. We did not use modified M-60's at the time.

OH-23 Raven Light Observation Helicopter

In 1948 the young aircraft designer Stanley Hiller developed the commercial Model 360 light helicopter as a test bed for his innovative 'Rotor-Matic' control system. This system, which used a hanging control column and small servo rotors mounted diagonally below the main rotor, provided excellent directional stability and for the first time allowed 'hands-off' helicopter flight. The Model 360 was refined into the Hiller commercial UH12A (a company, not military, designation), a three-place, open cockpit craft powered by a 200 hp Franklin engine. In the fall of 1950 the Army purchased a single UH-12A for evaluation and allocated the machine the designation YH-23A. This aircraft (serial 50-1254) differed from the standard commercial UH-12A in having only two seats, and was powered by a 178 hp Franklin engine.

The 4-place Hiller H-23 was based on the U. S. Navy UH-12, which was first flown in 1948. The H-23 Raven performed as a utility, observation, and MedEvac helicopter during the Korean war. Model numbers ranged A through D, F and G. The H-23A had a sloping front windshield. The H-23B was used as a primary helicopter trainer. Beginning with the UH-23C, all later models featured the "Goldfish bowl" canopy similar to the Bell model 47, and also featured the Bell-designed short weighted gyrostabilizer bar. The OH-23 had a speed of 97 mph (84 knots). The Raven had a two-bladed main rotor, a metal two-bladed tail rotor. Both the OH-23B and the OH-23C were powered by one 0-335-5D engine.

OH-23 Raven

The OH-23D was a purely military version with a 0-435-23C engine and a more reliable transmission. Most OH-23Ds were replaced by the OH-23G, the most common version of the Raven, with a more powerful Lycoming 0-540-9A six-cylinder, horizontally opposed, air-cooled 305 hp engine. The OH-23G could seat four. The MedEvac version carried two external skid-mounted litters or pods. The Raven saw service as a scout during the early part of the Vietnam war before being replaced by the OH-6A Cayuse in early 1968. The Raven could be armed with twin M37C .30 Cal. machine guns on the XM1 armament subsystem or twin M60C 7.62mm machine guns on the M2 armament subsystem. The XM76 sighting system was used for sighting the guns.

The type's successful performance during the evaluation led the Army to order one hundred production examples in October 1950, the largest single helicopter order placed by the Army up to that time. The nearly 1800 Ravens ultimately procured by the Arm were of the following variants:

H-23A: First production model, one hundred of which were delivered beginning in early 1951. The H-23A was essentially identical to the YH-23A, with the same powerplant, seating for two, and skid-type landing gear. Most H-23As were delivered to the Army in air ambulance configuration with one totally enclosed exterior stretcher pannier mounted on either side of the cabin. This variant saw extensive service during the Korean War in both the casualty evacuation and general utility roles.

H-23B: Generally similar to the H-23A, the -B model Raven differed from its predecessor in having a 200 hp Franklin (or, in some later model machines, a 250 hp Lycoming) engine, a combination skid and wheel landing gear, and various detail changes. The H-23B could also be fitted with stretcher panniers, though the majority of the 273 machines procured by the Army between 1952 and 1956 were not so equipped. More than half of all -B model aircraft were used as basic helicopter flight trainers at Fort Wolters, Texas. All surviving examples were redesignated OH-23B in 1962.

H-23C: Military version of the commercial Model UH-12C. This variant differed from the H-23B in having seating for three under a one-piece Plexiglas canopy, as well as in having metal, rather than wooden, rotor blades. The Army purchased 145 examples beginning in 1956, and those remaining in service in 1962 were redesignated OH-23C.

H-23D: This Raven variant differed from earlier versions in having a completely new rotor and transmission system, as well as numerous design changes intended to increase by some sixty percent the number of hours that could be flown between airframe overhauls. In addition, the H-23D was powered by a 250 hp Lycoming engine rather than the 200 hp Franklin power plants used in the H-23B and early model H-23Cs. The Army procured a total of 438 -D model Ravens, delivery of which began in 1956. The H-23D, which was redesignated OH-23D in 1962, was the Army's primary basic helicopter trainer until supplanted in that role by the Hughes TH-55 (q.v.) in the mid1960s.

H-23F: A military version of the commercial Model 12E-4, the H-23F was a four-place aircraft ordered by the Army in early 1962 specifically for use in Central and South America with the Army element of the Inter-American Geodetic Survey. All twenty-two machines acquired by the Army were powered by the 305 hp Lycoming VO-540-AlB engine, had extended cabin sections, and sported inverted-vee tailplanes on the boom just forward of the tail rotor. Though ordered with the H-23F designation most of these aircraft were delivered as OH-23Fs.

OH-23G dual control trainer - 793 of which were
acquired beginning in early 1962

H-23G: Essentially a three-place, dual control version of the H-23F, the G model was powered by the same 305 hp Lycoming engine. The Army procured 793 examples of this variant beginning in early 1962, and most were delivered with the Tri-Service designation OH-23G.

The H-23 Raven served the Army well in a variety of roles, and saw extensive combat duty in both Korea and Vietnam. The last H-23 in the regular Army, a -D model trainer (serial 57-3007) that had logged more than 100,000 accident-free miles at Fort Wolters, was retired from active duty and transferred to the Army Reserve in 1971.

Bell UH-1 Helicopter Gun Ships

The first three UH-1Ms were equipped with the Hughes INFANT (Iroquois Night Fighter and Night Tracker) system which used a low-light-level TV (LLLTV) and Infrared searchlight to aim the M21 armament subsystem. The M134 "Minigun" was equipped with flash suppressors and used a 9:1 ratio of ball to tracer ammunition because the normal ratio of 5:1 and muzzle flash blinded the LLLTV camera. The three aircraft were evaluated from December 1969 to February 1970 by the 227th Assault Helicopter Battalion of the 1st Cavalry Division (Airmobile). The INFANT equipped UH-1M was moderately successful when flown with two conventional gunships and a Command and Control "Slick". The INFANT was used to find and mark the target for the other gunships, but it was felt the AC-130A Hercules was a more capable aircraft for night operations.

The UH-1M was also equipped with the AN/AAQ-5 Forward Looking Infrared (FLIR) fire control system, a component developed for use on the AH-1G (SMASH) Cobra. The AN/AAQ-5 provided a televised thermal image which enabled the crew to detect, identify, and fire on ground targets during day or night operations. The M21 armament subsystem was integrated with the AN/AAQ-5 FLIR in positioning and fire control aspects.

The UH-1M could also be armed with an M5 40mm grenade launcher and M60D 7.62mm or M213 .50 Cal. pintle-mounted door guns on the M59 armament subsystem.

Tactical Air Support  - Part 1

1. BACKGROUND AND ENVIRONMENT.

a. TACAIR support available to ground commanders in the RVN far exceeds that which has been available in any past conflict in which US forces have been involved. The almost complete lack of sophisticated enemy air defense in the RVN has allowed the use of TACAIR en masse with extreme accuracy. TACAIR aircraft in use in the RVN are provided by the USAF, the USMC, the USN, the Royal Australian AF, and the VNAF. The Commander, 7AF, in his role as single manager for air in the RVN, controls all FWMAF and US TACAIR assets, except those of the USN. The Navy provides 7AF with a daily number of sorties that will be available for commitment and these aircraft are provided to 7AF for employment. The VNAF manages and controls all of its assets. However, US, FWMAF, and VNAF TACAIR assets are all controlled and single managed by a joint combined 7AF/VNAF TACC at Tan Son Nhut Air Base. Figure C-1 shows the geographical deployment and location of facilities which control and direct TACAIR in the RVN    .

b. In addition to the CAS provided to ground forces, 7AF conducts a DAS program designed as an interdiction campaign against enemy lines of communication and base areas in the RVN.

c. A most important type of air support, other than TACAIR, in the RVN is the massive B-52 strikes in a saturation bombing role. These B-52 strikes are under the operational control of SAC. The detailed planning of the B-52 strikes is done by SAC representatives at 7AF HQ. The decisions on where to place B-52 strikes are made at MACV.

d. Most TACAIR strikes are controlled by an airborne FAC. In the RVN, the FAC is airborne so that he can see both the target and the strike aircraft. He uses the O-1 Bird Dog, O-2A, and OV-10 Bronco light aircraft equipped with FM, VHF, and UHF radios and armed with flares and target-marking smoke rockets and smoke grenades. The other method of providing CAS is by the use of radar-controlled all-weather strikes, referred to as Combat Sky Spot. This method can be used under adverse weather conditions and at night and is executed similar to the B-52 strikes, i.e., with no warning to the enemy.

2. THE TACAIR CONTROL SYSTEM.

a. Introduction.

(1) TACS in the RVN is designed for comprehensive and responsive control of all TACAIR. It is a closely-knit composite of 7AF/VNAF/ USMC personnel, equipment, and operations centers. In addition to controlling 7AF, VNAF, and USMC (strike and reconnaissance only) air operations, the TACS coordinates and integrates USN and SAC operations in the RVN.

(2) A separate but allied system, the AAGS, provides for processing preplanned requests for air support and rapid exchange of battle information. The two systems, TACS and AAGS, so parallel each other that there is rapid coordination of all air and ground operations.

b. Organization of the TACS.

(1) The TACS has the characteristic and advantage of flexibility to fit any tactical situation. It provides for centralized direction while still permitting decentralized execution of specific operations. The system has proved its responsiveness to ground commanders; the reaction time to requests for immediate air strikes is usually less than 40 minutes.

(2) The TACS is centered around a joint combined VNAF/USAF/USMC operations center at Tan Son Nhut Air Base, the TACC. The schematic outline of this system is shown below, in Figure C-5.

Figure C-5 : Tactical Air Control System (TACS)

Its purpose is to coordinate and control the total US and RVN air effort. There are several units and agencies below the TACC level that are involved in daily execution of air-ground operations. The 7AF provides the equipment and the TACP personnel who work closely with ground commanders. The USMC uses its own equipment and personnel. There are four DASCs operationally subordinate to the TACC. Three of them are combined USAF/VNAF centers (I DASC, II DASC, and III DASC) which support US, FWMAF, and ARVN ground commanders in ARVN I CTZ, II CTZ, and III CTZ. There are no US or FWMAF ground forces supported by US TACAIR in ARVN IV CTZ and IV DASC is entirely under VNAF control.

(3) USAF TACPs, operating under each DASC, are positioned with the ARVN corps , divisions, and regiments and the I and II FFORCEV divisions and brigades, as shown below, in Figure C-6. The responsibilities and manning of the TACPs vary, depending on the level of assignment. Each TACP includes an ALO and/or FAC, radio operators, FAC aircraft, and a vehicle with UHF, VHF, FM, and SSB radios.

Figure C-6 :

(4) The USMC provides its own ALOs, TACPS, and FACs to work with its ground units.

(5) Radar coverage is basic to the operation of the TACS. Sites are located throughout the RVN for complete coverage. For radar control purposes, the RVN is divided into two sectors; each sector contains a large high-performance radar at a CRC. Aircraft track data at the CRC is augmented by similar information provided by outlying radars at CRPs. The USMC operates one CRP and several TPQ-10 sites (the USMC equivalent of the USAF MSQ-77 radar bombing equipment).

c. Functions and Operations of the TACC.

(1) The TACC, acting for the 7AF commander in his capacity as MACV Air Force Component Commander and the DEPCOMUSMACV for Air Operations, has responsibility for running the air war in the RVN. The TACC performs several functions:

(a) It plans, directs, and coordinates all US, VNAF, and FWMAF TACAIR operations in the RVN.

(b) It publishes fragmentary (frag) orders to the agencies concerned, including the lst MAW in I CTZ whose strike and recon aircraft are tasked by the TACC.

(c) It directs, monitors, and diverts strike aircraft as necessary.

(d) It establishes policies and procedures governing the operation of the TACS.

(2) The four DASCs are operationally subordinate to the TACC and serve primarily as extensions of the TACC. They provide a fast reaction capability to satisfy immediate requests from ground commanders for CAS, TACAIR recon, and emergency airlift (not considered further here). They also provide minute-to-minute coordination between the ground commanders in their area and supporting air elements, not only strike aircraft but recon, herbicide, PSYOP, and B-52 aircraft as well.

(3) To fill an immediate request, the DASC may, with Army/USMC approval, divert TACAIR from preplanned missions enroute to the target. In many cases there will be enough airborne aircraft on missions of lower priority to provide diverts, and these result in a quicker response than scrambled aircraft. With one exception, the DASCs do not have authority to scramble alert aircraft - I DASC is allocated USMC ground-alert aircraft for scramble purposes and need only inform the TACC of their launch. If a DASC cannot fill an immediate request by diverts within its area of responsibility, it will request the TACC to scramble ground-alert aircraft. The TACC may elect to scramble aircraft or to divert strikes from an adjacent CTZ.

(4) The TACP provides an AF communication system down to the brigade level. An ALO, who is a key member of the brigade commander's staff, heads the TACP. The ALO attends the brigade commander's meetings, briefs on air activity in the area of interest, and advises on the use and capabilities of TACAIR. Also, the ALO is a senior FAC and the supervisor of the FACs in his TACP. These FACs are AF pilots who perform several vital missions from their airborne positions in light observation aircraft. The FACS:

(a) Maintain close contact with local ground commanders.

(b) Help keep ground commanders in contact by providing airborne radio relays.

(c) Direct air strikes.

(d) Perform BDA and forward BDA reports.

(e) Perform VR during daily airborne patrols of their sectors.

(5) The radar and extensive communication network of the TACS make possible the quick responsiveness of the system. All aircraft on strike missions are picked up on radar and identification is usually established within five minutes after takeoff. Radar direction is provided to the pilot to the rendezvous point with the FAC. After the strike, radar contact is reestablished with the controlling radar facility for the return to base. Should an aircraft need emergency assistance, the radar network can provide vectors to the nearest suitable base or bailout area. Strike aircraft are also provided in-flight radar advice on possible conflicting air traffic and warnings on artillery fires.

CH-47 Chinook Cargo Helicopter

The Boeing Vertol (model 114) YCH-47A made it's initial hovering flight on 21 September 1961. The all-weather medium lift CH-47A Chinook first entered service in Vietnam about 1966. The CH-47A was powered by either Allied Signal Engines T55-L-5 or T55-L-7 engines. CH-47B was powered by two Allied Signal Engines T55-L-7C engines. Models CH-47A, CH-47B, and CH-47C, all utilized the same airframe, but later models featured upgraded engines. The CH-47B featured a blunted rear rotor pylon, redesigned rotor blades, and strakes along the rear ramp and fuselage to improve flying characteristics. The Boeing Vertol (model 234) CH-47C had a strengthened transmission, Allied Signal Engines T55-L-7C engines, or was upgraded to T55-L-11A 3802 shp engines, and increased range. The CH-47C could carry from 33 to 44 troops or 24 litters plus two medical attendants. All three models saw wide use during the Vietnam war. They replaced the H-21 Shawnee in the combat assault role. The Chinook has two three-bladed main rotors, two engines, and a speed of 173 mph (150 knots).

The CH-47B was the standard troop transport used by the 1st Cavalry Division in Vietnam. The Chinook could be equipped with two door mounting M60D 7.62mm machine guns on the M24 armament subsystem and a ramp mounted M60D using the M41 armament subsystem. A few CH47A "Go-Go Birds" were also used experimentally in the gun ship role. Some CH-47 "Bombers" were equipped to roll-out riot control gas or napalm onto Viet Cong bunker complexes from the rear cargo ramp. The CH-47 could be equipped with a hoist and cargo hook. The Chinook proved especially valuable in "Pipe Smoke" aircraft recovery missions. The "Hook" recovered about 12,000 aircraft valued at over $3 billion during the war.

See Also 159th ASHB

CH-47 Chinook

The CH-47 is a twin-engine, tandem rotor helicopter designed for transportation of cargo, troops, and weapons during day, night, visual, and instrument conditions. The aircraft fuselage is approximately 50 feet long. With a 60-foot rotor span, on each rotor system, the effective length of a CH-47 (with blades turning) is approximately 100 feet from the most forward point of the forward rotor to the most rearward point on the aft rotor.

Maximum airspeed is 170 knots with a normal cruise speed of 130 knots. However, speed for any mission will vary greatly depending on load configuration (internal or external), time of day, or weather conditions. The minimum crew for tactical operations is four, two pilots, one flight engineer, and one crew chief. For more complex missions, such as air assaults, commanders may consider using five crew members and add one additional crew chief.

Development of the medium lift Boeing Vertol (models 114 and 414) CH-47 Series Chinook began in 1956. Since then the effectiveness of the Chinook has been continually upgraded by successive product improvements, the CH-47A, CH-47B, CH-47C, and CH-47D. The amount of load a cargo helicopter can carry depends on the model, the fuel on board, the distance to be flown, and atmospheric conditions.

The CH-47A, first delivered for use in Vietnam in 1962, is a tandem-rotor medium transport helicopter. The Chinook's primary mission is moving artillery, ammunition, personnel, and supplies on the battlefield. It also performs rescue, aero medical, parachuting, aircraft recovery and special operations missions. On June 25, 1958 the Army issued an invitation for a General Management Proposal for the US Army Medium Transport Helicopter. Five aircraft selected Vertol to produce the YCH-1B as the Army’s new medium transport helicopter. In July 1962 DoD redesignated all U.S. military aircraft and the HC-1B was redesignated the as the CH-47A. Early production CH-47A’s operated with the 11th Air Assault Division during 1963 and in October of that year the aircraft was formally designated as the Army’s standard medium transport helicopter. In June 1965 the 11th Air Assault Division was redesignated as the 1st Cavalry Division (Airmobile) and readied for deployment to Vietnam. Chinooks from the 11th Air Assault formed the nucleus of the 228th Assault Helicopter Battalion which began operations in Vietnam in September, 1965. CH-47A’s deployed to Vietnam were equipped with Lycoming T55-L7 engines generating 2650 shp. The aircraft had a maximum gross weight of 33,000 pounds allowing for a maximum payload of approximately 10,000 pounds. The hot mountainous conditions of Vietnam limited the A models performance capabilities and generated a requirement for increased payload and better performance.

The CH-47B was introduced by Boeing after a production run of over 350 CH-47A’s . The B model introduced the Lycoming T55-L7C engine, a beefed up airframe, nonsymmetrical rotor blades, and the blunted aft pylon for better stability. Boeing began delivering the CH-47B in May of 1967 and eventually produced a total of 108 B models before production shifted to the CH-47C.

The CH-47C Chinook model has a maximum cargo hook capacity of 20,000 pounds. The CH-47C has only a single cargo hook below the center of the aircraft. When hooking a single load, soldiers use the main hook. They must coordinate closely with the aircrew as to which hooks to use when carrying multiple loads. The planning figure for the fore and aft hooks is 10,000 pounds each. The Army’s continued need for further performance improvements lead to the development of the CH-47C. Designed to meet an Army requirement to transport a 15,000 pound sling load over a 30 mile radius, the C model boasted an increased gross weight to 46,000 pounds, increased fuel capacity, the Lycoming T55-L11 engine developing 3750 shp, and addition structural improvements. The first C model flew in late 1967 and became the mainstay of the Chinook fleet until the advent of the CH-47D. Production of the C model continued until 1980 with improvements such as the crash worthy fuel system and fiberglass rotor blades being incorporated into the fleet.

The CH-47D was the result of June 1976 contract for a modernized Chinook. The Army recognized that that the Chinook fleet was rapidly reaching the end of its useful life and signed a contract with Boeing to significantly improve and update the CH-47. Three airframes, CH-47A, CH-47B, and a CH-47C, were stripped down to their basic airframes and then rebuilt with improved systems to provide three CH-47D prototypes. Improvements included upgraded power plants, rotor transmissions, integral lubrication and cooling for the transmission systems, and fiberglass rotor blades. Other improvements included a redesigned cockpit to reduce pilot workload, redundant and improved electrical systems, modularized hydraulic systems, an advanced flight control system, and improved avionics. The Chinook has two tandem three-bladed counter-rotating fiberglass rotors. The CH-47D is powered by two Allied Signal Engines T55-L-712 3750 shp turbo shaft engines and has a maximum speed of 163 mph (142 knots). The CH-47D was rolled-out in March 1979. The CH-47D carries twice the load of a CH-47A and has improved performance. The CH-47D can operate at night and in nearly all weather conditions. The CH-47D is equipped with an air-to-air refueling probe. The Chinook can accommodate a wide variety of internal payloads, including vehicles, artillery pieces, 33 to 44 troops, or 24 litters plus two medical attendants. The Chinook can be equipped with two door mounting M60D 7.62mm machine guns on the M24 armament subsystem and a ramp mounting M60D using the M41 armament subsystem. The "D" model can carry up to 26,000 pounds externally. The CH-47D has three cargo hooks: a center (main) hook and two additional hooks fore and aft of the main hook.

159th ASHB - Battalion Headquarters, Phu Bai, South Vietnam.

The 159th Assault Support Helicopter Battalion was formed in country to be command and control for the medium and heavy lift helicopter units in General Support of the division. The army concept during this time was that the division has assigned aircraft as internal assets, i.e., lift capabilities for combat troops. In addition there was gunship units which were in support of the aviation assets, and could also support ground troops if needed. 

Hueys were the main stay for moving troops, administratively and for combat missions. To assist in large administrative troop movements and to resupply the artillery, engineers and other units needing large heavy items moved, the 159th was established with 3 companies of Chinooks and a company (-) of CH-54 or Cranes. The CH-54 company was actually a platoon of 4 aircraft. the 478th Heavy lift company assigned to the 159th ASHB was based at Da Nang, RVN. It was commanded by a Major, had 4 aircraft and 8 - 10 commissioned and warrants assigned as pilots. It maintained a company headquarters and supply room as did all the other full size aviation companies. Their mission was general support of the entire division, as was the Chinooks assigned to the battalion. Because of the scarcity of aircraft, and the age of the pilots, these were the "Old Men" of aviation. Seldom seen, awe inspiring, even to other pilots. Due to the limitations of the Chinook during the late 1960's, C - engines limiting the Chinook to approximately 10,000 lbs of lift, the crane or CH-54 was the "Heavy" lift unit and used for Mini bulldozers, 155mm howitzer moves, recovery of Chinooks, etc. Later with the full "C" engines mounted on the Chinooks, the Chinook could outlift the CH-54 and caused its demise. Today, the D Model Chinook will lift more than the CH-54 could with a reduced amount of fuel.

The Battalion headquarters was organized in 1967 - 1968 to command and control the medium and heavy lift units. The 478th was assigned from the 1st Cav. Division, A and B company of Chinooks were formed from units already in country. (B company may have formed stateside and joined as a completed unit, this writer has no specific information on the formation of A and B companies).

The Battalion Headquarters consisted of the Battalion Commander (LTC), XO (Major, usually waiting on rotation stateside or to command a company), Personnel S-1 (CPT), Security (S-2), Operations and Liaison (S-3), and Supply / Logistics (S-4), Assigned to Supply was a Non Aviation Warrant as the property book officer. He was the ONLY non aviator assigned to the unit.

In addition to the primary staff, listed above, the Battalion level was assigned a Headquarters and Headquarters company. This was commanded by a captain, also an aviator. This unit housed all the personnel and records for the command element, clerks, drivers, staff officers, etc. This unit also provided vehicle support for all the staff sections, jeeps, maintenance, etc.

During this period, the battalion was also authorized two OH - 6 helicopters for command and control of aviation operations. These aircraft had a 2 man maintenance unit assigned to the Headquarters company. Minor maintenance was allowed at this level with all major support coming from one of the subordinate units or from the 5th Transportation Group assigned to the 101st Division. 5th Transportation Group did up to Divisional level maintenance. The Transition into the OH - 6, later the OH - 58 was accomplished at unit level by the unit training officer. One of the staff officers had the additional duty of Instructor Pilot for transitions into the OH-6.

All pilots were qualified in the Chinook, prior to being assigned to the battalion or one of its companies.

The Headquarters company was not authorized a mess facility for the unit and command. In our case, we were within walking distance to "C" company and used a combined mess facility to feed Headquarters and C company.

During this time, the S-2 at the 159th had the responsibility to coordinate with all units in the NW corner of the Support Base, 1 Chinook Company, two Huey Lift Companies, 1 signal Battalion, and run a roster for perimeter support and security. Members of all units were assigned to guard duty on the perimeter of the compound. Our section was approximately 3,000 meters. It surrounded all the units pulling guard duty, plus the ammunition supply point for the division. Inside the base, each unit would be responsible for having its own internal security patrols, as well as reactionary forces that could be gathered and sent to the base perimeter if needed as reinforcements.

Added duty for the troops assigned to each unit might very well mean a crew chief or flight engineer might go 2 - 3 days without sleep, fly all day, guard duty at night, fly the next day and pull maintenance on the aircraft as needed. 

Source :

Charles Lee, Section Leader/Platoon Leader/Motor Officer, C/159th ASHB, 101st Airborne Division, Bn S-2, 159^th ASHB, RVN '68 – '69.

ACH-47A Armed/Armored Chinook

Four armed/armored ACH-47A Chinooks were specially built by Boeing Vertol in late 1965. These four aircraft were originally fielded in Vietnam for a six-months test period as the 53rd Aviation Detachment. Following the test period, the unit was attached to the 1st Cavalry Division's 228th Assault Support Helicopter Battalion and redesignated as the 1st Aviation Detachment (Provisional). By February 1968, only one of the original four gunships was still flying. The ACH-47A Chinook "Guns-A-Go-Go", with a crew of eight, was armed with up to five M2 .50 Cal. or M60D 7.62mm machine guns (four XM32 window and one XM33 ramp mounted), and two fixed-mounted XM34 M24A1 20mm cannon and two M18/M18A1 pod-mounted 7.62mm "Miniguns", or two XM159B/XM159C 19-tube 2.75 inch rocket launchers, and a chin-mounted 40mm automatic grenade launcher on the M5 armament subsystem.

Weapons carried by the ACH-47

They also featured added armor protection for the crew and some critical components. They proved to be effective in the combat assault role, but were involved in several accidents and were difficult to maintain. The experiment was discontinued with the introduction of the AH-1G "Huey" Cobra in August 1967. Chinooks were more valuable for use as troop carriers. The AH-1G Cobra was fast enough to assume the escort mission, had greater loiter time over the target, and presented a much smaller target to small arms fire.

CH-37 Mojave Medium Cargo Helicopter

Initially procured in 1956, the Sikorsky (model S-56) CH-37A/CH-37B, with a crew of three, was a large medium lift transport helicopter. Clam shell doors in the nose provided access to a cargo compartment that could accommodate two jeeps or a 105mm howitzer. The Mojave could carry 26 troops or 24 litters in the MedEvac role. The CH-37 had a single five-bladed main rotor and a metal four-bladed tail rotor. The CH-37 was powered by two Pratt & Whitney R-2800-54 2100 hp piston engines and had a speed of 131 mph (114 knots). It was used for aircraft recovery in Vietnam.

CH-37 Mojave attempting to lift downed
CH-21Shawnee from paddy

CH-54 Tarhe 'Skycrane' Heavy Lift Helicopter

The Sikorsky (model S-64A) CH-54A/CH54B "Skycrane", with a crew of three, was designed for heavy internal or external lift of heavy bulk loads. It had a rear-facing pilot's seat to provide a clear view of the cargo. A hoist was provided to allow pickups and deliveries without landing. A lightweight van (universal pod) could be attached to the fuselage for use as a mobile command post, maintenance and repair shop, or as a Mobile Army Surgical Hospital (MASH). The field hospital was equipped with X-Ray, lab equipment, and blood bank. It was well lighted and air conditioned so surgery could be performed wherever it was needed. A "people pod" was designed to carry 45 combat-ready troops. The " Skycrane" served with the 1st Cavalry Division in Vietnam. The CH-54 was used in aircraft recovery operations when loads were too heavy for the CH-47 Chinook. It was also useful for offloading during ship-to-shore operations. The CH-54 could also be rigged to drop the large 10,000 lb. ‘daisy-cutter’cratering bomb used to create landing zones ("LZs") in dense jungle. The T-54A Tahre had a six-bladed main rotor, four-bladed metal tail rotor, was powered by two Pratt & Whitney T73 -P-1 4500 shp turbine engines, and had a speed of 128 mph (111 knots). The CH-54B was powered by two Pratt & Whitney T73-P-700 4800 sph turbine engines.

CH-54 "Skycrane" recovering Chinook

It was the proven value of the CH-47 and CH-54 in Vietnam that prompted the USA to order a much larger HLH (heavy-lift helicopter), the Boeing Vertol YCH-61A, with payload of 45,000 lb (20412 kg) in the initial version. As soon as the Vietnam involvement was over this seemingly important machine was cancelled.

CH-34 Choctaw Cargo and Light Tactical Transport Helicopter

The Sikorsky (model S-58) CH-34A/CH-34C, essentially a lengthened and more powerful version of the Sikorsky (model S-55) H-19 Chickasaw cargo helicopter, could carry 12 to 16 troops. It could carry eight litters in the MedEvac role. The U. S. Marine Corps version, UH-34, was the primary Marine utility/assault helicopter used in Vietnam. The Sikorsky (model S-58) was licensed and built in Great Britain as the "Wessex". The Choctaw had a single four-bladed main rotor and a four-bladed metal tail rotor. The CH-34C was powered by a single Curtis-Wright R-1820-84C 1425 hp piston engine and had a speed of 123 mph (107 knots).

OH-58A Kiowa Light Observation Helicopter

OH-58A Kiowa with M27 armament subsystem

Length : 41' (12m) Weight : 1,700lbs (765kg) Payload : 1,300lbs (585kg) Cruise Speed : 140mph (224kph) Range : 388 miles (622km)

The Bell (model 206A) OH-58A Kiowa was procured by the U. S. Army when the Light Observation Helicopter (LOH) program was reopened for an additional buy in March 1968. The OH-58A was first deployed to Vietnam in early Autumn 1969. The Kiowa operated with air cavalry, attack helicopter, and field artillery units. The OH-58A could also be configured as a troop transport, MedEvac, or for external lift missions using an external hook. Kiowa's were commonly paired with the AH-1G "Huey" Cobra. The Kiowa would fly low to draw enemy fire, "trolling" for fire, mark the target, and call in the Cobra to attack. The OH-58A Kiowa could be armed with the M27 armament subsystem, the port (left) side mounting M134 six-barrel 7.62mm "Minigun". However the vibration from the "minigun" was too great for the frame until it was rebuilt for the OH-58D Kiowa Warrior. The Kiowa could also be armed with the 40mm grenade launcher on the XM8 armament subsystem. The Kiowa had a two-bladed semi-rigid seesaw all metal main rotor and a two-bladed rigid delta hinge all metal tail rotor. The OH-58A was powered by a single Allison 250-C18 317 shp turbine engine and has a speed of 132 mph (115 knots).

The successor to the Hughes OH-6 "Cayuse" as the standard LOH (light observation helicopter), the Kiowa was built at so high a rate that no fewer than 2,200 were delivered to the US Army between May 1969 and the end of the American involvement in Vietnam. Kiowa's were in action in Vietnam by September 1969, swiftly becoming the preferred type for executive, liaison and light transport missions as well as undertaking all forms of reconnaissance and target acquisition.

Helicopter armaments/weapons

Structure of Air Cav Unit