The Liberty ships

The Liberty ships were cargo ships built in the United States during World War II. They were cheap and quick to build, and came to symbolize U.S. wartime industrial output. Based on vessels ordered by Britain to replace ships torpedoed by German U-boats, they were purchased for the U.S. fleet and for lend-lease provision to Britain. Sixteen American shipyards built 2,751 Liberties between 1941 and 1945, easily the largest number of ships produced to a single design.

The production of these vessels mirrored, at much larger scale, the manufacture of the Hog Island ship and similar standardized types during the First World War. The immense effort to build Liberty ships, the sheer number of ships built, and the fact that some of the ships survived far longer than the original design life of five years, make them the subject of much study.In 1940, the British Government ordered 60 tramp steamships from American yards to replace war losses and boost the
merchant fleet. This Ocean class were simple but fairly large (for the time) with a single coal-fired, 2,500 horsepower
(1.9 MW) reciprocating engine of obsolete but reliable design. Britain specified coal plants because it had plenty of
coal mines but no indigenous oil fields. The predecessor designs, including the Northeast Coast, Open Shelter Deck
Steamer, were based on a simple ship originally produced in Sunderland by J.L. Thompson & Sons in 1879, and widely
manufactured until the SS Dorrington Court of the 1930s. The order specified an 18 inch (457 mm) increase in draught
to boost displacement by 800 tons to 10,100 tons. The accommodation, bridge and main engine of these vessels were
located amidships, with a long tunnel to connect the main engine shaft to its aft extension to the propeller.

The design was modified by the United States Maritime Commission to conform to American construction practices and to
make it even quicker and cheaper to build. The U.S. version was designated EC2-S-C1 — Emergency Cargo, 2 = large ship.The new design replaced much riveting, which accounted for one-third of the labour costs, with welding. The order was
given to a conglomerate of West Coast engineering and construction companies known as the Six Companies, headed by
Henry J. Kaiser, and also adopted as the Merchant Marine Act design.Early on, each ship took about 230 days to build (Patrick Henry took 244 days), but the average eventually dropped to
42 days. The record was set by Robert E. Peary, which was launched 4 days and 15 1/2 hours after the keel was laid,
although this publicity stunt was not repeated. The ships were made assembly-line style, from prefabricated sections.
In 1943, three new Liberty ships were being completed every day. They were mainly named after famous Americans,
starting with the signatories of the Declaration of Independence. SS Stephen Hopkins, which sank a German commerce raider in a
ship-to-ship gun battle in 1942 and became the first American ship to sink a German surface combatant.