UH-1A

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 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 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 powertrain, gears, and rotorshaft, 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 shp engine.

(2) The second type of hybrid was the UH-1B with the "540" rotor, T53-L-11D 1100 shp engine upgrade, powertrain, 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 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 calibres 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 manoeuvrable, 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 analysed 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.