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.

However, it faced major drawbacks, including its high cost of $1 million (equivalent to 13 Patrol Boat, Rivers)[8][9] and unreliability.

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.

[13][17][18] It had a range of 165 nautical miles (306 km; 190 mi)[13] and endurance of seven hours[19] The Army hovercraft, called Air Cushion Vehicles, had more extensive modifications.

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.

[4] Only one ACV was outfitted with a grenade launcher, however, and the miniguns were removed to make space for more troops and cargo[24] because it was found to be effective only for suppressive fire.

[5] 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.

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,[26]: 15  although using small arms was dangerous because spent casings could fall into the propeller.

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,[30] destroying 70 of their sampans and an equal number of their structures,[30] taking many prisoners,[17] and capturing their supplies.

[17] 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.

[30] 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.

The Army acquired the vehicles and activated their unit, the 39th Cavalry Platoon, in January before deploying them to Vietnam in April.

[6] 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.

[5]: 4  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.

[5] Fuel resupply was another frequently cited issue for longer missions,[10] especially given that no adequate method of refueling in the field existed.

[25] Troops riding in and on the PACVs also needed training to use them safely: during evaluation, one soldier died when he fell into the hovercraft's intake,[24] and another lost his hand to the propeller.

[25] This maintenance requirement, which was made even worse when the vehicles suffered damage,[36] combined with the insufficient firepower to lead an Army evaluation to conclude that "there is no hope of the [PACV/ACV] unit fighting to a satisfactory conclusion in any large engagement.

[1] Though no one onboard was killed, 14 men were injured and the attack slowed the pace of ACV operations because of Army regulations stipulating that the hovercraft work in pairs to protect each other.

[12] The Coast Guard PACVs were modified to meet their requirements by replacing the .50 cal gun mount with an observation dome and adding a KAAR LN66 radar and search-and-rescue equipment.

[21] Coast Guard PACVs were crewed by 3—operator, radar operator and navigator, and search-and-rescue crewman—and could carry 6 passengers and half a ton of cargo.

[11] Because it was lighter than the military version, the Coast Guard ACV could go up to 70 knots (81 mph; 130 km/h) and had a range of 300 nautical miles (350 mi; 560 km).

[11] However, they were also used to service buoys, resupply and repair remote lighthouses and lightships, enforce laws, clean up oil spills, and ferry personnel and supplies.

[11] The ACV was fast enough that it was able to respond to search-and-rescue calls while servicing buoys, something that was not possible for regular Coast Guard cutters.

It sank on 23 November 1971 after only 26 hours of operation in Lake Huron, after the cabin was breached by a rock and the engine inexplicably failed, leading the craft to take on water and sink.

[40] As such, the two surviving ACVs were transferred to US Army Mobility Equipment Research and Development Center in Fort Belvoir, Virginia, on 25 April 1975.