U-boat is an anglicised version of the German word U-Boot [ˈuːboːt] (listen), a shortening of Unterseeboot, literally "underseaboat. " 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 First and 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) and enforcing a naval blockade against enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from Canada and other parts of the British Empire, and from the United States to the United Kingdom and (during the Second World War) to the Soviet Union and the Allied territories in the Mediterranean. German submarines also destroyed Brazilian merchant ships during World War II, causing Brazil to declare war on the Axis powers in 1944.
On Jan. 13, 1942, German U-boat attacks officially started against merchant ships along the Eastern Seaboard of North America. From then until early August, Nazi U-boats dominated the waters off the East Coast , sinking fuel tankers and cargo ships with impunity and often within sight of shore.