Welcome to Assault Craft Unit (ACU) 4, the parent unit for landing craft air cushions (LCACs), which provide fast, over-the-horizon movement from ship-to-shore of combat troops and equipment through the surf zone and across the beach. ACU 4 has the same responsibilities for the LCACs that ACU 2 has for LCUs. However, unlike the LCUs, LCACs have no indigenous crew accommodations. With the Passenger Transportation Module (PTM), LCACs can carry up to 150 Marines at speeds of up to 30 knots. LCACs are deployable from landing helicopter assault (LHA) ships, landing helicopter dock (LHD) ships, and dock landing (LSD) ships.