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Air Cushioned Vehicle
(ACV) SK-5 

   The air cushioned vehicle (ACV) was developed by Bell Aerosystems in the late 1950s.  The ability to move quickly over land and water using a cushion of air left other vehicles and watercraft behind, and caught the attention of the Army and Navy. 

   Bell first developed the US Navy's Patrol Air Cushion Vehicle (PACV “Swift Boat”) based on a modified British design SR-N5.  The Navy's PACV first arrived in Vietnam as a unit in 1966.

   The Army worked with Bell to develop it's own version of the ACV in February 1968.  It was wider, longer and carried more weapons than the Navy PACV.  It also had stronger side decks and the front door of the cabin was widened to accommodate soldiers with gear.

   It had a turbine-powered, turbo shaft GE engine, a Hamilton 3-bladed, variable pitch, fully reversible propeller, and a centrifugal, 7 foot diameter, 12-bladed blower fan.

line drawing of ACV

cockpit of ACV


specs of ACV

 SK-5s to Vietnam

   The Army ACV unit deployed to Vietnam in May 1968, with three ACVs - hull numbers 901, 902, and 903.  The unit was initially stationed at Dong Tam, and later relocated to Ben Luc, under the control of the 9th Infantry Division.

9th ID patch

Patch of the
9th Infantry Division


   ACV 901 and 902 were in assault configurations with a full weapons load.  ACV 903, although identical to her sisters, was a transport variant and armed with only window mounted M-60 machineguns.  The .50 caliber machine guns and 40mm grenade launcher were not installed, to save room for carrying troops in the cabin.

ACV-903 pulling guard duty on the Plain of Reeds, 1969.

ACV in reeds

   The ACV unit conducted a variety of different missions:  training, supply, patrol, reconnaissance, assault and ambush.  They were also a blocking force in infantry sweeps.

    In execution of these missions, the ACV unit developed tactics.  They found working in pairs to be preferable to operating alone.  This allowed for the ACVs to offer support in case one got into trouble.

   When using two or three ACVs together, especially in land operations, an experienced crewmember flying in a helicopter to coordinate movements was preferred. 

   Once operations began, troops chose to ride on the outside hull rather than inside the cramped cabin.  They could move around easier, disembark faster, and add their personal weapons to the ACVs firepower in a firefight.

   This led to the full assault configuration of ACV 903, to match ACV 901 and 902.

ACV underway aerial view of ACV

     Because the ACV unit was a one-of-a-kind unit, they faced unique difficulties.

   The first was training.  There were only 24 men assigned to the unit.  They had to train their own replacements for operating and maintaining the ACV.  This required that one craft was kept aside for 14 days during each month.

   The second was unexpected maintenance and repair caused by battle or accidents.  There was no in-country support organization for maintenance or replacement parts until late 1969.  This support had to come from the states.

   For 8 months in 1969, ACV 901 was unavailable because of an accident which severely damaged the rear of the ACV.  In April 1969, only one serviceable engine was available for the ACVs; the other five were en route to or from servicing in the states.  Only during June 1968 were all three in operation.

patch of ACV

Unofficial patch and logo

    In late 1969, the ACV unit was assigned to the 20th Transportation Company, 34th General Support Group for maintenance and logistical support, and the Marine Corps agreed to service the engines at Phu Bai.

   In 1970, control of the ACV unit was assigned to the 3rd Brigade, 9th Division, as the rest of the 9th Division redeployed to the US.  The ACV unit adopted the unofficial designation as the 39th Cavalry Platoon (ACV).

One of the SK-5s at Dong Tam, January 1969

ACV in action

   The ACV unit stayed in Vietnam until the fall of 1970.  ACV #901 was destroyed in January 1970, and ACV #902 was destroyed in August 1970.  ACV 903 was returned to the states and is on display at the Transportation Museum.

ACV refueling

Above, the SK-5 refueling.  Note the deflated rubber skirts.  Dong Tam, 1969.

ACV at Dong Tam

Above, an SK-5 arriving with fully inflated skirts.  Dong Tam, Vietnam, January 1969.

  * * * 


   While conducting a combat operation in July 1968 in support of a South Vietnamese CIDG (Civilian Irregular Defense Force) unit and US infantry advisors, the Army SK5s were engaged in a 7-hour continuous fight with enemy forces.

   ACV 902 and 903 were assigned as a blocking force for a large scale operation being conducted by 3rd Brigade, 9th Infantry Division, in an area surrounded by canals on three sides.

   During the reconnaissance sweep, the SK5 boats inspected over 60 houses along the waterline and discovered over 25 bunkers within the area.

   After destroying the bunkers with their supporting infantry, the two hovercraft came under enemy fire.  Both craft returned fire, but were unable to press the attack since the CIDG forces were unwilling to dismount into a potential ambush.

   After disengaging, both ACVs repositioned to another area and were once again taken under fire. Both vessels returned fire and when the infantry inspected the area they discovered several killed enemy soldiers.

ACV in reeds

    At 5pm, the ACVs were returning to their temporary base at My Phouc Tay when they spotted a group of enemy soldiers in the open.  The Viet Cong (VC) were caught by surprise by the hovercraft and when engaged, they were unable to fade into the foliage as before.

   The boat crews called for infantry and air support, but were unable to get either due to the onset of nightfall.  Both ACV 902 and 903 fought the enemy soldiers, who were in open bunkers until their ammunition supply was exhausted.  Some soldiers and crewman of the boats were wounded in the firefight and both boats received battle damage from automatic weapons fire and mortars. 

   After seven hours of repeated engagements, the two SK5 hovercraft retired to their base to tend to the wounded and effect repairs.


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