The submarine was one of the most effective offensive naval craft of the war and was used to great advantage by the United States against the Japanese in the Pacific and by the Germans against Allied convoys in the Atlantic and the Mediterranean.

At the start of the war, the United States had 114 submarines. In the Pacific, 22 fleet boats operated out of Pearl Harbor, and 23 fleet boats and 6 older S-boats were based at Manila Bay in the Philippines. Sixty-three additional submarines of various classes were based along both U.S. coasts.

Figure 12-3 An American submarine officer scanning the surface.

Photo courtesy of the National Archives (80-G-11258)

The fleet boats were large, long-range submarines built in the decade before the war to protect surface ships. They were more than 300 feet long and equipped with ten 21-inch torpedo tubes and a stock of up to twenty-four torpedoes. They were also armed with a single 76-mm deck gun and several machine guns. The smaller S-boats were not as spacious as the larger subs, could not dive as deep, and were armed with only four torpedo tubes.

At the onset of the war in December 1941, U.S. submarines in the Pacific were ordered to search for and destroy Japanese merchant ships rather than support the surface fleet, as originally intended. But the mission was impeded by recurring problems with faulty torpedoes, a situation that was not completely remedied until 1943.

The first successful U.S. submarine attack occurred just a week after Pearl Harbor, when the Swordfish sank the Japanese merchant ship Atsutasan Maru off Indochina. On January 27, 1942, the Gudgeon became the first U.S. submarine to sink a Japanese warship when it successfully torpedoed the submarine I-173. The attack was one of many based on information derived from decoded Japanese naval communiqués. Over the course of the war in the Pacific, U.S. subs sank nearly 1,300 Japanese merchant vessels, 4 fleet and 4 escort carriers, a battleship, 12 cruisers, 42 destroyers, 22 undersea craft, and 2 Soviet merchant ships mistaken for Japanese vessels.

Smaller older American submarines patrolled the east coast of the United States and the Panama Canal Zone during the early days of the war, though they saw little action. Then, in the summer of 1942, Roosevelt responded to a request by Winston Churchill and ordered six fleet-type submarines to the Atlantic, to be based in Scotland. The subs participated in the invasion of North Africa, but poor weather and confused recognition signals resulted in the Gunnel and the Shad being attacked by friendly fire.

German submarines — called U-boats — patrolled the Atlantic during the early months of the war, sinking a great many Allied supply ships and dramatically affecting the European war effort. They played an integral role in the Battle of the Atlantic and were slowed only after the development of radar and increased use of antisubmarine ships and planes.

The first U-boats were launched in 1935 in direct violation of the Treaty of Versailles. When the war began, Germany had fifty-seven U-boats in commission, twenty-six of them large enough for ocean patrol. Their numbers increased quickly, and the German U-boat soon became the scourge of the Atlantic, which it easily accessed after the fall of Norway and France in 1940. By the end of 1942, nearly a hundred U-boats were in operation, with more to follow.

Germany and the Allies played a continual game of catch-up when it came to the U-boat, with every new submarine advance being met with a countermeasure. Germany also designed larger, better armed, and better equipped submarines such as the Type XXL, but few were produced, and they had little influence over the course of the war.