U-boat is the anglicised version of the German word U-Boot [ˈuːboːt] , a shortening of Unterseeboot, literally “undersea boat”. While the German term refers to any submarine, the English one (in common with several other languages) refers specifically to military submarines operated by Germany, particularly in the Firstand Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role (commerce raiding), enforcing a naval blockadeagainst enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from Canada, the British Empire, and the United States to the islands of the United Kingdom and (during the Second World War) to the Soviet Union and the Allied territories in the Mediterranean.
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 U.S. 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 vaunted role of Rosie the Riveters 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 a handful remain in 2015, two as operational museum ships.