Liberty ship

SS John W. Brown, one of three surviving operational Liberty ships, photographed in 2000
Class overview
Name:	Liberty ship
Builders:	18 shipyards in the USA
Cost:	US$2 million ($34 million in 2017)
Planned:	2,751
Completed:	2,710
Active:	1 (Traveling Museum Ship)
Preserved:	3
General characteristics
Class and type:	Cargo ship
Displacement:	14,245 long tons (14,474 t)
Length:	441 ft 6 in (134.57 m)
Beam:	56 ft 10.75 in (17.3 m)
Draft:	27 ft 9.25 in (8.5 m)
Propulsion:	Two oil-fired boilers triple-expansion steam engine single screw, 2,500 hp (1,900 kW)
Speed:	11–11.5 knots (20.4–21.3 km/h; 12.7–13.2 mph)
Range:	20,000 nmi (37,000 km; 23,000 mi)
Capacity:	10,856 t (10,685 long tons) deadweight (DWT)
Complement:	38–62 USMM 21–40 USNAG
Armament:	Stern-mounted 4-in (102 mm) deck gun for use against surfaced submarines, variety of anti-aircraft guns

The Liberty ship was a class of cargo ship built in the United States during World War II. Though British in conception, the design was adapted by the United States for its simple, low-cost construction. Mass-produced on an unprecedented scale, the now iconic Liberty ship came to symbolize U.S. wartime industrial output.

The class was developed to meet British orders for transports to replace those torpedoed by German U-boats. The vessels were purchased both for the U.S. fleet and lend-lease deliveries of war materiel to Britain and the Soviet Union. Eighteen American shipyards built 2,710 Liberty ships between 1941 and 1945, easily the largest number of ships produced to a single design.

Their production mirrored on a much larger scale the manufacture of the Hog Islander and similar standardized ship types during World War I. The immensity of the effort, the sheer number of ships built, the role of female workers in their construction, and the survival of some far longer than their original five-year design life, all make them the subject of much continued interest.

Only three Liberty Ships are preserved, two as operational museum ships.

In 1936, the American Merchant Marine Act was passed to subsidize the annual construction of 50 commercial merchant vessels which could be used in wartime by the United States Navy as naval auxiliaries, crewed by U.S. Merchant Mariners. The number was doubled in 1939 and again in 1940 to 200 ships a year. Ship types included two tankers and three types of merchant vessel, all to be powered by steam turbines. Limited industrial capacity, especially for reduction gears, meant that relatively few of these ships were built.

In 1940 the British government ordered 60 Ocean-class freighters from American yards to replace war losses and boost the merchant fleet. These were simple but fairly large (for the time) with a single 2,500 horsepower (1,900 kW) compound steam engine of obsolete but reliable design. Britain specified coal-fired plants, because it then had extensive coal mines and no significant domestic oil production.