The Patrol Air Cushion Vehicle (PACV), also known as the Air Cushion Vehicle (ACV) in Army and Coast Guard service, was a United States Navy and Army hovercraft used as a patrol boat in marshy and riverine areas during the Vietnam War between 1966 and 1970. Six hovercraft were built, three for the Army and three for the Navy.
The military developed the PACV because its lack of draft meant that it could operate unimpeded in the shallow and reed-choked waters widespread in South Vietnam, most notably in the Mekong Delta and Plain of Reeds. The PACV was also found to be valuable because of its unusually high speed of , faster than other watercraft in the conflict. However, it faced major drawbacks, including its high cost of $1 million (equivalent to 13 Patrol Boat, Rivers) and unreliability. During the conflict, two of the Army's three hovercraft were destroyed by the Viet Cong. The PACVs in Vietnam were considered "unsuccessful" in evaluations and were withdrawn in 1970. Following their service in Vietnam, the Navy PACVs returned to the United States where they were used by the Coast Guard, where another sank in an accident.
Development The PACV was based on the Bell Aerosystems SK-5 hovercraft; a licensed version of the British Saunders-Roe (later, British Hovercraft Corporation) SR.N5 hovercraft. The SK-5 was adapted for American military use in 1965. Three were purchased by the US Navy for operations in the emerging Vietnam War. Training of PACV crews was performed in the waters off Coronado, California near San Diego. Design of the Army ACVs began in 1966 and was completed
Design Two different designs were made: one for the Navy and one for the Army. The Navy's hovercraft, called Patrol Air Cushion Vehicles, more closely resembled the civilian SK-5s that they were based on while the Army craft had more extensive modifications. Each hovercraft was long, with a beam of and a height of when floating on its air cushion. It weighed fully loaded. Army and Navy PACVs had a crew of 4—driver, radar operator, and gunners—and could carry up to 12 troops, many of whom rode on the outside of the vehicle.
Both designs were powered by a General Electric 7LM100-PJ102 gas turbine engine. The engine, its 304-gallon (1,150 litre) fuel tank, an auxiliary power unit, and the Westland transmission were located amidships. The engine powered both the three-blade variable-pitch propeller for thrust and the diameter centrifugal fan for lift. The transmission served to link the engine and lift fan so that the fan could provide lift and thrust. Twin rudders and elevators sat behind the fans. As a hovercraft, the PACV could skim over water, including shallow and reed-choked waters, flat land, and ice. The PACV/ACV was very fast compared to contemporary watercraft, being capable of speeds up to . It had a range of and endurance of seven hours
The Army hovercraft, called Air Cushion Vehicles, had more extensive modifications. They had heavier armor and reinforced, load-bearing decks. Army ACVs carried of armor—roughly equal to that of an M113 armored personnel carrier. The armor was thickest around the engine, transmission, and fuel tanks, providing protection from .50 caliber rounds fired at , while the armor around the crew compartment could only block .30 caliber rounds fired at . To save weight, many crews removed the armor around the crew compartment, and an Army evaluation recommended that it be removed altogether because of it "did not provide any protection to the crew," especially against heavier weapons such as recoilless rifles, artillery, and RPGs.
The communications package consisted of a six-station intercom system, UHF radios, and a radio security set. The boats were shipped with AN/ARC-54 FM radios. However, these proved unreliable, with an operational ready rate of only 35 percent. Army units sought to replace them with VRC-125s. While it is not known if this replacement occurred, one ACV did receive a VRC-46 radio. The hovercraft carried a Decca 202 radar with a dish antenna, which could detect targets within . Some Army ACVs were fitted with XM3 Personnel Detectors (better known as XM-3 "people sniffers"), which could detect human emissions including carbon and ammonia. This equipment was used to find hidden enemies. Dog teams were also sometimes carried to help detect enemies. The radar was found to be very effective, including for navigating in low-visibility and foggy conditions.
The PACV was armed with twin .50 caliber M2 Browning machine guns in a roof-mounted turret in the front and two 7.62mm M60 machine guns, one port and one starboard. The Army initially equipped their hovercraft with a minigun and 40 mm M5 automatic grenade launcher as well. Only one ACV was outfitted with a grenade launcher, however, and the miniguns were removed to make space for more troops and cargo because it was found to be effective only for suppressive fire.
The Army ACVs had other improvements over the Navy PACVs beyond their additional armor, namely a wider cockpit, more horsepower, two gun positions instead of one, and a flat deck on top of the skirt for troops to ride on.
Operational history
PACVs were first deployed to Vietnam in May 1966 as PACV Division 107, Task Force 116, where they were used by the Navy for riverine patrol missions in the Mekong Delta and on the Mekong River. Often called "Pac Vees", they were armed with a .50 caliber machine gun mounted on a rotating platform in the front and two side-mounted M60 machine guns. In addition, the crew, and often US Army Special Forces and ARVN Rangers, riding on the side panels, employed assorted small arms such as M16 rifles and M79 grenade launchers as well as various other rifles, .45 pistols, light and medium machine guns, and grenades, although using small arms was dangerous because spent casings could fall into the propeller. The PACV was used to prevent Viet Cong infiltration from the sea and tidal areas along river mouths and deltas. It was especially useful in shallow marshy areas, especially the Mekong Delta, where other patrol boats such as the Patrol Boat, River or Patrol Craft Fast (Swift boat) could not go.
The PACV's relatively light weight of only seven tonnes meant that it could be easily carried by a CH-54 helicopter. This allowed it to be airlifted between forward operating bases or transported back to base when it suffered damage. The PACV could also be split into sections and then transported in Air Force transport planes, which was how they were brought to Vietnam.
Navy PACVs were deployed in Operations Game Warden and Market Time, the Navy's operations to deny Viet Cong access to resources in the Mekong Delta and prevent North Vietnamese weapons, fighters, and supplies from entering South Vietnam, respectively. The PACVs were deemed unsuitable for Operation Game Warden because of their "mechanical unreliability" and the limitations imposed on them by terrain. As a result, they were removed from the operation and transferred to another Navy unit, CTF 117. They were also found unsuitable for Market Time operations after serving in that operation from 20 September to 17 October 1966, due to their high noise, low visibility, high cost, and limited utility on the high seas or in narrow waterways. In November 1966, the Navy PACVs were used to great effect in Operation Quai Vat (Vietnamese for "Monster", which was what the Viet Cong called the PACVs). In the operation on the Plain of Reeds, conducted jointly with Vietnamese Civilian Irregular Defense Group (CIDG) troops and Army helicopters and special forces, the PACV force brought its speed and firepower to bear on the Viet Cong, killing at least 23 of them, destroying 70 of their sampans and an equal number of their structures, taking many prisoners, and capturing their supplies. This demonstration of combat prowess in the marshy terrain in southwestern Vietnam formed the basis for stationing the Army ACVs in the Plain of Reeds along the South Vietnamese/Cambodian border. An Army evaluation found that in the Plain of Reeds, "any mission requiring ground operations can best be accomplished by ACV unts," particularly reconnaissance, light assaults, infantry transport, canal security, cordoning off areas to prevent escape, and patrolling. Though the loud noise of the PACVs was an issue, their speed made up for it in this otherwise difficult terrain, especially during the monsoon season. The PACV could clear rice paddy dikes and other solid obstacles up to high and negotiate slopes of up to . However, the PACV did not perform well in the dry season, with an Army evaluation noting that "The wetter the season, the better for vehicle operations".
The Navy withdrew the PACVs for overhaul in January 1967 and redeployed them to Vietnam in early 1968. Also in 1968, the Army began employing its version of the PACV, the ACV. The Army acquired the vehicles and activated their unit, the 39th Cavalry Platoon, in January before deploying them to Vietnam in April. There were only three Navy PACVs and three Army ACVs during the whole Vietnam War. Two of the three ACVs (No. 901 and 902) were Assault Air Cushion Vehicles (AACV), weapons-heavy vessels configured for attack missions, while the other (No. 903) was a Transport Air Cushion Vehicle (TACV) configured for logistics missions. The TACV only carried the twin M60s, forgoing the .50 cal and other weapons to increase space in the cabin for carrying troops. Both AACVs were lost to Viet Cong attacks. Navy PACVs were based out of Cat Lo Naval Base and operated by Task Forces 116 and 117. The three Army ACVs were operated by the 39th Cavalry Platoon, 9th Division, and were based out of Ben Luc and Đồng Tâm Base Camp, although they often deployed from fire support bases.
The Green Berets stationed in Moc Hoa became proponents of the PACVs, using them in many of their early operations. Search and destroy raids conducted out of Moc Hoa in November 1966 caught the Viet Cong by surprise and resulted in many Viet Cong deaths.
The PACV's speed, maneuverability, and firepower lent themselves to many types of missions, including patrolling, search and destroy, escorting other ships, raiding, reconnaissance, medical evacuation, transporting artillery pieces, and providing fire support to infantry. It was best suited for ambushes and raids, especially at night, when it could be easily concealed behind reeds and swamp grass. Although it was too loud to be very effective at surprise attacks, it could use its speed to raid Viet Cong bases and escape before they could react. The PACV was found to be most effective when employed in combined arms operations alongside helicopters, artillery, and other watercraft; patrol missions conducted in concert with air cavalry or Hurricane Aircat airboats were found to be especially effective. The PACV's low profile and radar also meant that it was used as a stealthy stationary radar station when its engines were off. However, Army evaluations found that the ACV had insufficient firepower, being unable to damage armored or fortified targets, and recommended that it be outfitted with heavier weapons such as TOW missiles, 20mm autocannons (such as the M139 or M61 Vulcan), or 106mm M40 recoilless rifle. They also found that it could be too loud to be used effectively for patrol and interdiction missions. Fuel resupply was another frequently cited issue for longer missions, especially given that no adequate method of refueling in the field existed.
The PACV was frequently compared to a helicopter because of its speed, terrain crossing ability, maintenance requirements, and cost. Army ACV units operated similarly to air cavalry.