U-boat resupply. U-564 is resupplied with torpedoes from another U Boat whilst in the Caribbean in early August 1942.
U-Boat (Ship Type) German submarine. The word is a shortened form of Unterseeboot, which means “undersea boat” in German. Germany’s foremost naval weapon in both world wars was the submarine. Especially in World War I, it nearly cut the crucial ocean supply lines to Great Britain. From the beginning of World War I to the end of World War II, U-boats accounted for the sinking of almost 8,000 merchant ships and warships with the loss of hundreds of thousands of lives. But they were vulnerable: 962 U-boats were lost by the end of World War II, taking some 33,000 seamen (half of all crewmen) to the bottom.
In World War I, Germany was the first nation to mount a combination of torpedo tubes and a deck gun on its boats and fit them with superior periscopes and wireless sets. The use of batteries combined with diesel propulsion paved the way for long-range strikes against enemy targets. Such craft were taken by Allied powers for study after the war, becoming the basis for most World War II submarine fleets. Even during the 1940s Germany led the way in submarine technology with the development of the homing torpedo and the schnorkel, although, perhaps ironically, it was the U.S. Navy in the Pacific theater in World War II that was the most effective practitioner of submarine warfare.
The scene of extensive German U-boat operations from the beginning of World War II to May 1943. Germany surrendered all its U-boats at the end of World War I but during the interwar years violated the Treaty of Versailles and had submarines built in neutral countries, drafted mobilization plans, and established schools for submarine deck officers and engineers. Unfortunately for Germany, Adolf Hitler and his naval commander, Admiral Erich Raeder, planned to build a balanced fleet by 1948, with the result that instead of the 300 U-boats demanded by Submarine Service commander Admiral Karl Dönitz, Germany had but 57 submarines, of which 27 were oceangoing types, on 1 September 1939.
Nonetheless, during the war German U-boats came close to cutting Allied North Atlantic communications lines. The German navy listened to Allied radio traffic, and Dönitz used the information thus obtained to direct his boats to where he believed enemy ships would be. His success was reduced in part because Luftwaffe commander Herman Göring would not provide planes to reconnoiter at sea and because Hitler often directed U-boats to engage in missions that they were not designed to undertake. Yet single U-boats, and then wolf packs resupplied at sea by supply boats (“milk cows”), had nearly severed maritime communications between the United States and the beleaguered British Isles by the early spring of 1943.
The success of Dönitz’s tactics was proved by the sinkings accomplished in the first year of the war by such aces as Otto Kretschmer, Wolfgang Luth, Gunther Prien, Joachim Schepke, Herbert Schultze, and Erich Topp. U-boat losses, however, led Dönitz to stress the use of wolf packs. He placed great reliance on the very maneuverable Type VII U-boat: 625/745 tons (surfaced/submerged), diesel-electric drive, speed of 16 knots surfaced/submerged, range of 4,300 kilometers surfaced, and armament of 5 torpedo tubes and 6 reloads as well as 2 deck guns. These and other types were not fitted with effective radar until almost the end of the war, and their magnetic torpedo detonators often failed, but at least during the first year of the war they could operate farther west in the Atlantic than the Royal Navy could escort convoys.
Forty-two U-boats supported the German naval forces that invaded Norway in the spring of 1940. In addition to having bases in Norway, after 22 June 1940 Dönitz had U-boat bases built along the Atlantic coast of defeated France, thus sparing the boats the dangerous long journey from Germany through the North Sea and around Scotland to reach the Atlantic and increasing the time they could remain on station. At the cost of 31 submarines lost, Dönitz’s U-boats sank much of the 1.11 million tons of British merchant shipping that was destroyed in the northwestern Atlantic in the latter half of 1940. U-boats would trail convoys until dark and then attack. The 27 boats Italy sent to the South Atlantic beginning in July 1940 had slim pickings.
The Allies meanwhile increased warship, merchant ship, aircraft, and blimp production programs, and they relied on radio direction-finding stations ashore and afloat, radar on ships and aircraft, sonar, improved depth charges, and brilliant floodlights (the Leigh Light) on aircraft. The British stopped using fleet carriers for convoy escort after losing two of them, but in the fall of 1940 the United States gave Britain 50 old destroyers. After that, the British had support groups leave convoys to attack nearby U-boats, and the United States fitted aircraft with rockets and antisubmarine ships with forward-thrown shipborne antisubmarine “hedgehogs,” or “mousetraps” (small depth charges Britons called Squids). It helped the Allies that in the spring of 1941 Dönitz instituted “tonnage warfare,” a strategy of sinking ships wherever they were found. This meant that a U-boat might go after an unloaded freighter instead of a more important tanker.
The Allies gained greatly after the United States entered World War II. U.S. industrial might provided many warships and merchant ships. For convoy work, the United States provided hunter-killer groups—an escort carrier escorted by about 5 destroyers or new destroyer escorts. But 81 ships were sunk along the U.S. Atlantic coast by the 19 U-boats Dönitz dispatched beginning in February 1942. Finally the organization of convoys led in May to the U-boats being redirected southward.
Dönitz also sent some large boats to operate in the South Atlantic and the Indian Ocean, but supply problems and attacks by surface ships caused their recall. Meanwhile, British and American convoys to Murmansk, Russia, reduced the number of warships operating against U-boats in the Atlantic and Mediterranean.
The nadir for the Allied convoys occurred between the summer of 1942 and spring of 1943. In March 1943 British, Canadian, and U.S. representatives met in Washington and, among other things, agreed that Britain and Canada would assume responsibility for convoys north of 40 degrees and the United States for those to the south and for troop convoys entering the Mediterranean. The United States in addition would provide Canada very long-range (VLR) planes to reconnoiter a large area in the Central Atlantic in which U-boats hid and would provide at least one hunter-killer group for convoy work. Moreover, Chief of Naval Operations (CNO) and Commander in Chief U. S. Fleet Admiral Ernest J. King had his operations officer, Rear Admiral Francis S. “Frog” Low, head a “phantom” Tenth Fleet—a brain center for antisubmarine warfare (ASW). It had no ships but could give orders to any vessel, and its research and publications were of great use to all the Allies.
The tide now began to turn against Dönitz. Particularly effective against his boats were aircraft fitted with shortwave 10 cm radar the Germans could not detect. Increased Allied radio direction-finding stations often ordered convoys to change course to evade suspected U-boats while aircraft utilized floodlights to illuminate and attack the boats. The Allies lost 36 ships in the Atlantic in May, but Dönitz lost as many as 41 boats, a third of those at sea. Moreover, Allied ships and aircraft were sinking his boats all over the Atlantic and in the Bay of Biscay—and Germany was losing the war on land.
Dönitz counted on success from a radar receiver; acoustic torpedo; new propelling plant; new small, speedy coastal submarines; and improved deck guns with which to fight Allied aircraft. No radar receiver appeared until the end of the war; the acoustic torpedo was countered with noisemakers that attracted it away from ships’ screws; aircraft guns, rockets, and depth charges overcame U-boat guns; the new submarines appeared too late; Allied radar could pick up the schnorkel tubes fitted to some boats; and the Allied produced so many ASW ships that they overwhelmed the numbers of U-boats.
May 1943 was Dönitz’s “Black May,” a month from which his submarine campaign never recovered. He was responsible for that result, primarily because the Allies homed in on his radio signals not only to his boats in the North Atlantic but to those recalled from the South Atlantic and the Indian Ocean and sent forces to attack those boats.
By February 1944 few U-boats could survive in the North Atlantic. The Russians largely forced German submarines out of the Baltic, and American and British forces made U-boat operations in the Bay of Biscay extremely dangerous. The Western Allies invaded France with little U-boat opposition.
Bekker, Cajus D. Hitler’s Naval War. Garden City, NY: Doubleday, 1974.
Busch, Harald. U-Boats at War. London: Putnam, 1955.
Morison, Samuel Eliot. United States Naval Operations in World War II. Vol. 1. The Battle of the Atlantic, September 1939–May 1943. Vol. X. The Atlantic Battle Won, May 1943–May 1945. Boston: Little, Brown, 1947–1956.