By Joseph Trevithick
(Photos courtesy of U.S. Army Aviation Museum via Ray Wilhite)
In 1955, the Bell Aircraft Corporation won a contract to provide a new utility helicopter to the U.S. Army. Eventually designated the UH-1, derivatives of the basic design remain in service today in a wide array of capacities and are one of the most recognizable helicopters around the world. The design became iconic of the conflict in Vietnam, being used as both a transport and as the U.S. Army’s first real gunship.
The use of the helicopter in the latter role, however, was largely unintentional. Bell began development of the helicopter at a time when the U.S. Army was just beginning to explore the concept of arming helicopters. Early exercises involving provisional armed helicopter units gave mixed results, and led many to question their validity. While the Army persisted with armed helicopters, it also investigated the potential for developing an organic fixed wing close air support capability. Opposition from the fledgling Air Force led to the abandonment of that plan.
As the first preproduction helicopters, designated first XH-40 and then YH-40, began arriving in the late 1950s, the U.S. Army still had no plans to officially authorize armament for them. It was not until November 1960 that a proposal was made for the basis of issue of armament kits for units receiving the new helicopters, by that time designated HU-1A (from this designation the helicopter also gained its now well known nickname: “Huey”). The proposal was not approved. Still, the new doctrine of airmobility was winning more and more support and it was becoming clear that armed helicopters would be a key element of this.
Between 1960 and 1962, various Army commands and individual units worked on developing the airmobile doctrine and weapons for its primary vehicle. The lack of a unified effort both helped and hampered these developments. As of 1961 the U.S. Army was investigating three armament subsystems for standardization with regards to the HU-1A: the XM138, the XM153, and a system commonly referred to as the XM11.
The XM138, developed by General Electric beginning in 1961, was a nose turret fitted with a single 40mm XM75 automatic grenade launcher. This new weapon fired relatively low velocity high-explosive projectiles at a modest rate of fire. Ammunition was fed to the weapon from a magazine in the main cabin by way of a flexible feed chute. The chute charted a circuitous route from a port on the aircraft’s left side between the main cabin door and the cockpit door, which then ran under the cockpit door and to the nose before snaking up and then down to feed into the weapon. The turret capable of limited traverse, elevation, and depression was controlled by a sight unit in the co-pilot’s position. The weapon could also be fixed forward and fired by the pilot.
The XM153 was a suppressive fire subsystem consisting of two sponsons, each with two 7.62mm M73 machine guns. Developed by Emerson Electric starting in 1958, the subsystem was intended to be a universal armament option for all Army utility and transport helicopters, with the sponsons capable of being fitted to the H-21, H-34, and H-1 families of helicopters. The XM153 designation eventually came to refer to the basic components of the kit, with the helicopter specific mounting hardware receiving new designations. The mounting hardware for the HU-1A, which allowed one sponson to be fitted to either side of the aircraft, was designated XM156. Ammunition again fed from magazines inside the main cabin via flexible feed chuting snaked through ports in the aircraft’s fuselage. The XM153 also featured a hydraulic control system allowing the weapons to be traversed, elevated, and depressed, by way of a flexible sight unit in the co-pilot’s position. The weapons could also be fixed forward and fired by the pilot.
Interested in a capability to take out point targets and enemy armor, the U.S. Army had also acquired a subsystem that allowed for the carriage of six Nord SS.11 missiles. Official sources disagree as to whether this system ever received a designation, but it is commonly referred to as the XM11. This was possibly an informal reference to the manufacturer’s designation for the missile. In 1962, however, the SS.11 missile received the designation AGM-22 in the unified designation system for aircraft, rockets, and missiles. The designation XM11 was not otherwise used for any other armament subsystem and is used here for clarity. This system, developed by Bell in 1959, was attached to aircraft’s fuselage and featured two outrigger booms, each with three launch rails. The booms could be folded vertically when not in use for storage and transport purposes. The SS.11 missile was an early wire-guided missile and was optically tracked using a flare at the rear and guided to its target by way of a joystick in the co-pilot’s position.
Parallel to these efforts, various Army commands and units, such as the Army Aviation School’s the 7292nd Aerial Combat Reconnaissance Company (Experimental), also continued work on experimental armament kits. The 7292nd Aerial Combat Reconnaissance Company, referred to commonly as the ACR Company was commanded by Colonel Jay D. Vanderpool and had evolved from the original “Vanderpool’s Fools,” which had started exploring helicopter armament in the 1950s.
In 1958, Hayes Aircraft Corporation had installed an armament subsystem that had been developed by the U.S. Army’s Rock Island Arsenal using 4.5” spin stabilized rockets on an H-34 helicopter. This followed a similar system fabricated and installed at Rock Island Arsenal on an H-21 helicopter. Both of these systems had been passed to the ACR Company. In 1961, a variant for the HU-1A helicopter, consisting of two eight-tube assemblies mounted on either side of the aircraft, was supplied to the ACR Company for testing.
The ACR Company also tested a combination of the XM11 armament subsystem and .30 caliber machine guns on the HU-1A. The gun portion consisted of a .30 caliber AN/M2 machine gun on a mount with a fixed magazine and feed assembly on each of the aircraft’s landing skids. The mounting hardware for the guns was similar to that used on the experimental KX-13 armament subsystems developed for the H-13 family of helicopters. Further work on such combinations was stopped when the Army’s Combat Developments Command dictated that armament subsystems consist of only one type of weapon, such as missiles, rockets, machine guns, or grenade launchers.
Troop D, 1st Squadron, 1st Cavalry, the “air cavalry” troop of the divisional cavalry squadron of the 1st Armored Division, a new component of U.S. divisions under the ROAD force structure, also conducted independent experiments in arming the new HU-1B helicopter’s in its lift section. These included a single .30 caliber or .50 caliber gun mounted on a recoil absorbing mount on each side of the aircraft fitted to the aircraft’s hardpoints. .30 caliber AN/M2 and .50 caliber AN/M2 and M3 machine guns were used in the experiments. The guns could be elevated up to fifteen degrees, to compensate for the aircraft pitching downward in forward flight, and were pneumatically charged and electrically fired via solenoid trigger. In the .30 caliber arrangement, each gun fed from seven hundred round magazines fixed to the mount, while in the .50 caliber arrangement the guns each fed via flexible feed chuting from four hundred round magazines in the main cabin. A variant was also developed that combined the .30 caliber guns with four twelve-tube 2.75” rocket pods, two on each side of the aircraft stacked on top of each other.
Perhaps most importantly, however, the U.S. Army had activated the Utility Tactical Transport Helicopter Company (Provisional), commonly referred to as the UTTHCO, in Okinawa, Japan in 1962. The unit initially received HU-1A helicopters, but no armament. The unit was subsequently deployed to the Republic of Vietnam as part of the military assistance mission there. The unit quickly developed its own improvised armament for the helicopters consisting of the relatively common arrangement of skid-mounted .30 caliber machine guns. The UTTHCO used M37 machine guns, feeding linked ammunition straight from open magazines in the main cabin. Jams were common and a bar was fabricated fixed to the gun’s charging handle that allowed a crew chief seated on the cabin floor to re-cock the weapon’s in flight. To provide additional firepower, eight-tube 2.75” rocket pods were fabricated by combining four two-tube MA-2 pods together, which were then attached to the rear of the landing skid. Chief Warrant Officer Clarence J. Carter, who had previously been a part of the ACR Company at Fort Rucker, was responsible for the design of these weapons. The weight of the armament seriously overload the helicopter and crews noted that to get airborne the helicopters often had to be flown down the runway like conventional aircraft before enough lift could be achieved to get off the ground.
In December 1962, the UTTHCO received its first UH-1B. In 1962, the U.S. military had also instituted a new designation system for all the services resulting in the HU-1 family of aircraft being re designated as UH-1s. These new B model aircraft featured a more powerful engine and improved rotor system over the older As, and those aircraft sent to the UTTHCO also featured a new factory armament subsystem, the XM6E3. A further development by Emerson Electric of the XM153, the XM6 series replaced the M73 machine guns with new M60C machine guns. The XM6E2 design had been mounted directly the aircraft fuselage in front of the main cabin doors like the older XM153. The XM6E3 utilized the aircraft’s hardpoints and the Bell designed Universal External Stores Pylon to mount the subsystem, an arrangement that allowed rapidly swapping it out in favor of other subsystems depending on the situation. The system was otherwise comparable to the XM153.
Still seeking additional firepower, the same eight-tube rocket launchers used on the UH-1As were modified to ride on top of the XM6E3’s sponsons. The ACR Company fabricated a similar improvised solution to the XM6E3 kits it received, the Combat Developments Command having relaxed its development restrictions. The XM6E3 was eventually standardized as the M6, the only member of the family to see use.
What had become clear from the experience of the UTTHCO was that the idea of armed troop transport helicopters might be a difficult proposition. In addition, the existing helicopters available were not necessarily suitable for use as either light transports or gunships. Evaluations in 1963 by the Joint Operational Evaluation Group – Vietnam had even called into question the viability of armed helicopters as a concept and had suggested that fixed wing aircraft would remain more suited to providing close air support and escorting airmobile forces. The Army determined that a modified UH-1B could be an interim solution until a suitable dedicated platform could be developed. The result was a modified UH-1B with a further improved engine and rotor system, the same used on its new long-fuselage UH-1 variant, the UH-1D. UH-1s were subsequently readily divided into short and long fuselage types. In an evaluation in 1964, the U.S. Army pitted this new UH-1C against Kaman’s UH-2, coming to the conclusion that neither aircraft was suitable for the mission. The Army subsequently initiated the Advanced Aerial Fire Support System (AAFSS) program, which would lead to the abortive AH-56A Cheyenne attack helicopter.
In the meantime, with no other options for its new airmobile units and other helicopter units across the Army, the UH-1B and UH-1C aircraft remained tasked with the gunship role, and as a result work continued on improving armament options for them. The UTTHCO had acquired Aero 15C bomb racks in 1963 from U.S. Air Force units and the unit’s Major Luther Lawler and Chief Warrant Officer Cleatus Heck had combined them with the XM6E3 subsystem and the Bell Universal Pylon. A subsystem utilizing two Aero 15C racks on either side of the aircraft and no fixed guns was also tested. This four-rack setup was developed by Chief Warrant Officer Clemuel H. Womack, who had previously served with Troop D, 1-1st Cavalry and had been responsible for leading much of the developments there. His creations for the UTTHCO, like those for the 1st Armored Division, were generally referred to as “Womack Kits.”
The use of standard aircraft bomb racks allowed the attachment of a broader selection of typical aircraft ordnance, such as U.S. Air Force 2.75” rocket launchers. Nineteen-tube LAU-3/A pods were found to be too heavy, but seven-tube LAU-32A/A pods were found to be of suitable weight. However, both pods had been designed for use by high performance aircraft and to be entirely disposable. Their flimsy structural design meant that using the pods more than once was dangerous. Gun pods and tanks for dispensing chemical smoke screens were also carried.
Seeing these developments, Emerson Electric had begun development in 1963 of a factory standard armament subsystem to combine the two types of weapons. The subsystem, designated the XM16 and eventually standardized as the M16, combined the guns of the M6 with a so-called Universal Mount, designated the M156 (not to be confused with the older XM156 armament subsystem). The mount included a MA-4A bomb rack and was designed to be rapidly inserted between the Bell Universal Pylon and the armament sponsons. The MA-4A again allowed the use of standard aircraft ordnance, but was intended in the M16 subsystem to be used with a seven-tube 2.75” rocket pod.
By 1966, Emerson had developed an entire line around the basic components of the M6 system, but using a wide array of weapons, including the 40mm M75 automatic grenade launcher and the M134 machine gun, a rifle-caliber rotary barreled gun developed by General Electric from larger aircraft cannon designs and dubbed the “minigun.” These included the XM9 (one M75 grenade launcher on either side of the aircraft), the XM20 (one M134 machine gun on either side of the aircraft), and the XM21. The systems used the same sighting equipment as the M6.
The XM21, standardized as the M21, combined the XM20 subsystem with the M156 Universal Mount. In the XM20 and M21 subsystems, the ammunition arrangement was modified from that used on the M6 and M16. As there were only two guns instead of four, the four magazines were linked together into two pairs of magazines using an adapter that included a booster motor to help ammunition feeding. A single feed chute then fed ammunition from the main cabin to each of the guns. Also, while all subsystems in Emerson’s M6 family featured a safety mechanism, in which the weapons would stop firing if traversed inboard enough to potentially shoot into the aircraft fuselage. The XM20 and M21 subsystems added an additional feature. Firstly, the externally powered M134s were rigged to fire at a rate of fire of three thousand rounds per minute. If the safety mechanism engaged on one of the guns, the subsystem increased the power to the other to increase the rate of fire to six thousand rounds per minute, in effect providing the same volume of fire.
Other existing systems were also improved upon and standardized for broad usage. A variant of the XM11 making use of the Bell Universal Pylon was designated the M22. A product improved version of the XM138 was also introduced, designated the XM5, which was type classified as the M5 in 1964. This improvement on the XM138 fed ammunition from a central magazine straight through the nose instead of the previous route and featured an improved turret design that fully enclosed the weapon. Two magazines were available for the system. A rectangular box type held one hundred and fifty rounds of high velocity 40mm ammunition, while a larger cylindrical type held three hundred and fifteen rounds. The M75 within could be elevated fifteen degrees and depressed thirty-five, and the turret itself could traverse sixty degrees left or right.
The new system was not without its problems. A report in 1964 declared the basic launcher design unsafe. The operation of the M75 allowed for live rounds to be left in the breech after firing had ceased, creating a dangerous situation. Improvements were made to correct this, but the operator’s manual for the UH-1B, which included a section on the system, had a note on how to deal with a “runaway launcher” that would not stop firing. The relatively low velocity of the so-called “high velocity” grenades also meant that it could be hard to register hits from a fast moving aircraft on rounds fired anywhere but straight ahead. In addition, the rounds were armed by spinning in flight after being fired and the rotor downwash could interfere with this leading to unreliable performance. These reasons also affected the use of 40mm automatic grenade launchers as door guns on transports and gunships. None of these issues were ever entirely resolved, even after the introduction of the improved M129 grenade launcher, and by the time the AH-1S Cobra gunship had been introduced in the 1970s, the U.S. Army had determined that if the 40mm grenade launcher on that helicopter was to be used, if it was fitted at all, the helicopter’s chin turret had to first be in the locked forward position.
In addition to utilizing the UH-1B and UH-1C in the gunship role, the Army had also worked on expanded artillery options for its new airmobile units. Work on so-called “aerial rocket artillery” had begun in the early 1960s and initially envisioned helicopters fitted with rocket launchers as akin to self-propelled howitzers. The helicopters could be expected to fly to suitable firing positions and then fire indirectly while landed at enemy targets like a towed or self-propelled rocket launcher. Eventually this doctrine became more akin to the use of gunships, with the aircraft providing direct fire. The process for requesting aerial rocket artillery fires would remain similar to that for traditional indirect artillery, however.
These aerial rocket artillery helicopters were authorized the M5 armament subsystem along with the M3 armament subsystem. The latter consisted of two twenty-four round 2.75” rocket pods fitted to the Bell Universal Pylon, one on each side of the aircraft. The rockets were fired in pairs to maintain balance and could be fired using fixed reflex sights by either the pilot or the co-pilot. Aerial rocket artillery units were also authorized a limited number of M22 armament subsystems.
It was soon found that aircraft armed with the M3 subsystem would often return not having expended all of their rockets. This combined with the fact that the rocket pods were heavy and cumbersome and the individual tubes could be removed for servicing eventually led to banks of tubes being removed in some instances. Warrant Officer Robert Maxwell of the 2nd Battalion, 20th Artillery was also responsible for developing a field modification that involved removing a single bank of tubes from each pod and modifying a portion of the M22 subsystem so that a single launch rail was fitted to each of the pods. The combination subsystem, dubbed the Maxwell System, allowed for a single aircraft to carry thirty-six 2.75” rockets along with two AGM-22 missiles.
The ability to rapidly install or remove the various armament subsystems from the aircraft meant that units often obtained armament subsystems not necessarily authorized to their unit type. M3 armament subsystems, for instance, appeared in numerous assault helicopter companies. Field modifications and other improvisations were also common. Some of the first units slated to receive the M21 armament subsystem in 1966 for instance were provided with M18 gunpods, which also utilized the M134 minigun, as a way of familiarizing these units with the new weapon. These pods were used in conjunction with the M16 armament subsystem, meaning the aircraft flew with an armament of four M60C machine guns and two M134 machine guns. Door gunners were often utilized on short fuselage UH-1s as well, generally using infantry type or modified infantry type M60 machine guns mounted on the Sagami mount or suspended by a bungee cord from the aircraft’s cabin roof. The Sagami mount, developed at the Army’s Sagami Depot on Okinawa, featured a swing arm with a pintle that could either be fitted directly to the aircraft’s hardpoints or to the front end of the Bell Universal Pylon.
Official experimentation also continued. The Army had long been interested in seeing whether a suitable 20-30mm weapon could be combined with the UH-1 gunship concept. General Electric had proposed an arrangement using a single 20mm M61 Vulcan rotary-barrel cannon on a fixed forward firing mount, but this had not passed rigorous testing. Also tested were modified three-barrel versions, predecessors to the M197 cannon, as door guns. Other 20mm weapons in the U.S. military supply chain, such as the M39 and M139, were also tested in this position. In all instances the weapons proved to be too strenuous on the aircraft.
The Army had also looked at using the single-barrel 20mm M24 cannon in a forward firing arrangement, and this showed more potential. The initial prototypes saw a single cannon on a simple open mount fitted to each side of the aircraft. The later variants, designated XM31, featured an enclosed pod for the weapon. Ammunition for the early and late variants fed from magazines in the main cabin via flexible feed chuting, through the cabin roof and then down into the pod. Each gun had a five hundred round ammunition supply.
The Army also investigated using the 30mm XM140 cannon, developed by the U.S. Army’s Weapons Command. The XM30 armament subsystem was seen as a possible replacement for the M3 armament subsystem in the aerial artillery role and featured flexible mounts on each side of the aircraft, each with a single XM140 cannon. The fully enclosed mounts could be elevated twelve degrees, depressed forty-five, and traversed right and left five degrees. As on the XM31, ammunition fed from the main cabin through the roof and then down into the mount.
Even with the introduction of the AH-1 family of dedicated gunship helicopters in 1966, which were themselves also seen as an interim solution until the AH-56 could be put in service, short fuselage UH-1 gunships soldiered on. Army units in Vietnam still had UH-1 gunships into the 1970s. In 1972, during the Easter Offensive, the Army even dispatched two UH-1B aircraft from Army Missile Command to Vietnam to help counter the North Vietnamese Army. These older helicopters were the only aircraft in the Army at the time fitted with the TOW missile system and the events of 1972 were seen as a perfect opportunity to test the weapon in an operational environment. The 1st Combat Aerial TOW Team (Provisional) served admirably and the XM26 armament subsystem, consisting of a sight unit in the co-pilots lower front window and two three-tube missile launchers on each side of the aircraft, proved its worth. The operational experience of the XM26 would inform the development of the TOW missile system for the AH-1 family.
The short fuselage UH-1s gunships remained significantly underpowered under the weight of their armament, however. When the Army tested the Iroquois Night Fighter and Night Tracker (INFANT) system in 1970, it realized that the combination of the M21 armament subsystem and the AN/ASQ-132 night vision image intensifier system would so degrade the performance of the UH-1C that a new upgrade was required. The resulting helicopter, designated the UH-1M, most notably paired the UH-1C aircraft with the engine from the new long fuselage UH-1H, which had begun to replace the UH-1D. While the upgrade became widely applied to the short-fuselage UH-1 fleet, it became most well known for its connection to the INFANT program, leading some to believe that this was the only usage of the type.
As it happened, UH-1M helicopters remained in service as gunships and as utility helicopters in the active Army at least into the late 1970s and in the Army National Guard well into the 1990s. Armament was largely standardized around the M5 and M21 armament subsystems, though the M22 armament subsystem also remained in service. The Army even assigned a designation, XM50, to the combination of the M5 and M21 armament subsystems, but this appears to have been rarely if ever used. Many were converted to QUH-1M target drones and met relatively inglorious ends after years of service. Others were used by the so-called “Opposing Force” or OPFOR as surrogates for enemy helicopters during training exercises until being replaced by modified JUH-1Hs. Others found new homes abroad. Ten were sent to Laos in the 1970s where they were operated briefly by Thai “volunteers” before the fall of the country to the Pathet Lao in 1975. Beginning in 1985, El Salvador received a significant number of ex-US Army National Guard UH-1s, including UH-1Ms. No other countries are known to have received UH-1Ms. Many Salvadoran UH-1Ms were scrapped after the civil war ended in 1992, but some continue to serve in their Air Force as gunships to this day. The last UH-1Ms and QUH-1Ms were only completely phased out of the U.S. Army in the 2000s, bringing to a close the era of the short-fuselage UH-1 in this country.
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