Operation Ivory Soap was a classified United States military project to provide forward theatre support for aircraft repair and maintenance during World War II in the Pacific Theatre of Operations. Six Liberty ships were converted into floating shops to repair aircraft. They were designated Aircraft Repair Units (Floating). The Liberty ships were retrofitted to repair B-29 bombers. Eighteen smaller 187 feet (57 m) long auxiliary vessels were designated as Aircraft Maintenance Units. The smaller vessels were intended to repair fighter aircraft like the P-51 Mustang, Lockheed P-38, Sikorsky R-4 helicopters, and amphibious vehicles.