A total of 388 APA (troop) and AKA (cargo) attack transports were built for service in World War II in at least fifteen classes.
Some of these were outfitted with heavy boat davits and other arrangements to enable them to handle landing craft for amphibious assault operations.
In 1942, when the AP number series had already extended beyond 100, it was decided that these amphibious warfare ships really constituted a separate category of warship from conventional transports.
Some attack transports were assigned to the European Theatre, participating in the invasions of North Africa, Sicily, Italy and Normandy.
This created extreme logistics burdens for the invasion force because it resulted in considerable overloading of the transports with both men and equipment.
The last of these were decommissioned in 1980 and sold abroad, leaving only a few thoroughly obsolete World War II era hulls still laid up in the Maritime Administration's reserve fleet.