3. Several Liberty ships were modified for specific roles
Until FDR led them to be tagged as Liberty ships, the vessels bore the designation of Emergency Cargo Ships. Given the bureaucratic penchant for obscure designations, the first Liberty ship bore the official identity of EC2-S-C1. “EC” referred to Emergency Cargo; “2” to the length of the hull at the waterline (between 200-450 feet). “S” referred to steam propulsion and “C1” to the design itself. As construction continued, several variants developed. Ships built to serve as colliers (coal ships) substituted “AW1” for “C1”. Others bore the designations of “C2”, “C3” and so on, for ships which served as tankers, those designed specifically to carry tanks and armored vehicles, and others designed to carry disassembled aircraft in their holds. To the general public, they were all Liberty ships.
In 1944 six Liberty ships were acquired by the Army Air Forces, though they remained crewed by the United States Merchant Marine. These ships were converted to serve as aircraft maintenance facilities, which themselves were operated by the Army Transport Service. The ships were part of then classified Project Ivory Soap, a support effort for the B-29 Superfortress bombers based on Guam and Tinian. They were among the first American ships to include landing decks for helicopters. They were also among the first ships to evacuate casualties via helicopter transport. The Army officially designated them as ARUs (Aircraft Repair Unit, Floating). During 1944 other Liberty ships were modified to accommodate larger numbers of heavy trucks, required to support the Allied forces in Europe following the invasions in Normandy and Southern France.