World War II: Battle of the Atlantic

This lengthy battle at sea occurred throughout the entirety of the war

The convoy ship SS Pennsylvania Sun burns after being struck by a torpedo in the North Atlantic, July 15, 1942

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The Battle of the Atlantic was fought between September 1939 and May 1945 throughout the entirety of World War II.

Battle of the Atlantic Commanding Officers


  • Admiral Sir Percy Noble, RN
  • Admiral Sir Max Horton, RN
  • Admiral Royal E. Ingersoll, USN



With the British and French entrance into World War II on Sept. 3, 1939, the German Kriegsmarine moved to implement strategies similar to those used in World War I. Unable to challenge the Royal Navy's capital ships, the Kriegsmarine began a campaign against Allied shipping to cut off British supply lines. Overseen by Admiral Raeder, German naval forces sought to employ a mix of surface raiders and U-boats. Though he favored the surface fleet, which would come to include the battleships Bismarck and Tirpitz, Raeder was challenged by his U-boat chief, then-Commodore Doenitz, regarding the use of submarines.

Initially ordered to seek out British warships, Doenitz's U-boats had early success sinking the old battleship HMS Royal Oak at Scapa Flow and the carrier HMS Courageous off Ireland. Despite these victories, he vigorously advocated for using groups of U-boats, called "wolf packs," to attack the Atlantic convoys that were resupplying Britain. Though the German surface raiders scored some early successes, they drew the attention of the Royal Navy, who sought to destroy them or keep them in port. Engagements such as the Battle of the River Plate and the Battle of the Denmark Strait saw the British respond to this threat.

The Happy Time

With the fall of France in June 1940, Doenitz gained new bases on the Bay of Biscay from which his U-boats could operate. Spreading into the Atlantic, the U-boats began attacking British convoys in wolf packs further directed by intelligence gleaned from breaking the British Naval Cypher No. 3. Armed with the approximate location of an approaching convoy, they would deploy in a long line across its anticipated path. When a U-boat sighted the convoy, it would radio its location and coordination of the attack would commence. Once all of the U-boats were in position, the wolf pack would strike. Typically conducted at night, these assaults could involve up to six U-boats and forced the convoy escorts to deal with multiple threats from several directions.

Through the remainder of 1940 and into 1941, U-boats enjoyed tremendous success and inflicted heavy losses on Allied shipping. As a result, it became known as Die Glückliche Zeit ("the happy time") among the U-boat crews. Claiming over 270 Allied vessels during this period, U-boat commanders such as Otto Kretschmer, Günther Prien, and Joachim Schepke became celebrities in Germany. Key battles in the second half of 1940 included convoys HX 72 (which lost 11 of 43 ships in the course of fighting), SC 7 (which lost 20 of 35), HX 79 (which lost 12 of 49), and HX 90 (which lost 11 of 41).

These efforts were supported by Focke-Wulf Fw 200 Condor aircraft, which aided in finding and attacking Allied ships. Converted from long-range Lufthansa airliners, these aircraft flew from bases in Bordeaux, France and Stavanger, Norway to penetrate deep into the North Sea and Atlantic. Capable of carrying a 2,000-pound bomb load, Condors typically would strike at low altitude to bracket the target vessel with three bombs. Focke-Wulf Fw 200 crews claimed to have sunk 331,122 tons of Allied shipping from June 1940 to February 1941. Though effective, Condors were seldom available in more than limited numbers, and the threat later posed by Allied escort carriers and other aircraft ultimately forced their withdrawal.

Guarding the Convoys

Though British destroyers and corvettes were equipped with ASDIC (sonar), the system was still unproven, unable to maintain contact with a target during an attack. The Royal Navy was also hampered by a lack of suitable escort vessels. This was eased in September 1940, when fifty obsolete destroyers were obtained from the U.S. via the Destroyers for Bases Agreement. In spring 1941, as British anti-submarine training improved and additional escort vessels reached the fleet, losses began to lessen and the Royal Navy sank U-boats at an increasing rate.

To counter improvements in British operations, Doenitz pushed his wolf packs further west, forcing the Allies to provide escorts for the entire Atlantic crossing. While the Royal Canadian Navy covered convoys in the eastern Atlantic, it was aided by President Roosevelt, who extended the Pan-American Security Zone nearly to Iceland. Though neutral, the U.S. provided escorts within this region. Despite these improvements, U-boats continued to operate at will in the central Atlantic outside the range of Allied aircraft. This "air gap" posed issues until more advanced maritime patrol aircraft arrived.

Operation Drumbeat

Other elements that aided in stemming Allied losses were the capture of a German Enigma code machine and the installation of new high-frequency direction-finding equipment for tracking U-boats. With the U.S. entry into the war after the attack on Pearl Harbor, Doenitz dispatched U-boats to the American coast and Caribbean under the name Operation Drumbeat. Commencing operations in January 1942, the U-boats began enjoying a second "happy time" as they took advantage of unescorted U.S. merchant ships and America's failure to implement a coastal blackout.

Losses rising, the U.S. implemented a convoy system in May 1942. With convoys operating on the American coast, Doenitz withdrew his U-boats back to the mid-Atlantic that summer. Through the fall, losses mounted on both sides as the escorts and U-boats clashed. In November 1942, Admiral Horton became commander-in-chief of the Western Approaches Command. As additional escort vessels became available, he formed separate forces tasked with supporting convoy escorts. Not tied to defending a convoy, these forces could specifically hunt U-boats.

The Tide Turns

In the winter and early spring of 1943, the convoy battles continued with increasing ferocity. As Allied shipping losses mounted, the supply situation in Britain began to reach critical levels. Though losing U-boats in March, the German strategy of sinking ships faster than Allies could build them appeared to be succeeding. This ultimately proved to be a false dawn, as the tide rapidly turned in April and May. Allied losses dropped in April, yet the campaign pivoted to the defense of convoy ONS 5. Attacked by 30 U-boats, it lost 13 ships in exchange for six of Doenitz's subs.

Two weeks later, convoy SC 130 repelled German attacks and sank five U-boats while taking no losses. The integration of several technologies that became available in the previous months—the Hedgehog anti-submarine mortar, continued advances in reading German radio traffic, enhanced radar, and the Leigh Light—swiftly shifted Allied fortunes. The latter device allowed Allied aircraft to successfully attack surfaced U-boats at night. Other advances included the introduction of merchant aircraft carriers and long-range maritime variants of the B-24 Liberator. Combined with new escort carriers, these eliminated the "air gap," and with wartime ship construction programs like Liberty ships, they rapidly gave Allies the upper hand. Dubbed "Black May" by Germans, May 1943 lost Doenitz 34 U-boats in the Atlantic in exchange for 34 Allied ships.

Latter Stages of Battle

Pulling back his forces during the summer, Doenitz worked to develop and create new tactics and equipment, including U-flak boats with enhanced anti-aircraft defenses, a variety of countermeasures, and new torpedoes. Returning to offense in September, U-boats enjoyed brief success before again taking heavy losses. As Allied airpower strengthened, U-boats came under attack in the Bay of Biscay as they left and returned to port. With his fleet shrinking, Doenitz turned to new U-boat designs like the revolutionary Type XXI. Designed to operate entirely submerged, the Type XXI was faster than any of its predecessors, and only four were completed by the end of the war.


The final actions of the Battle of the Atlantic took place on May 8, 1945, just before German surrender. Allies lost around 3,500 merchant ships and 175 warships in the fighting, along with roughly 72,000 sailors killed. German casualties numbered 783 U-boats and around 30,000 sailors (75% of the U-boat force). Victory in the Atlantic theater, one of WWII's most important fronts, was critical to the Allied cause. Prime Minister Churchill later cited its importance:

"The Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea or in the air depended ultimately on its outcome."
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Hickman, Kennedy. "World War II: Battle of the Atlantic." ThoughtCo, Jul. 31, 2021, Hickman, Kennedy. (2021, July 31). World War II: Battle of the Atlantic. Retrieved from Hickman, Kennedy. "World War II: Battle of the Atlantic." ThoughtCo. (accessed March 25, 2023).