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.