Battle of the Atlantic in World War II

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

USS Pennsylvania Sun Burning
Aerial view of burning convoy ship SS Pennsylvania Sun after being struck by a torpedo in the North Atlantic, July 15, 1942. PhotoQuest / Getty Images

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

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 September 3, 1939, the German Kriegsmarine moved to implement strategies similar to those used in World War I. Unable to challenge the Royal Navy in regard to capital ships, the Kriegsmarine began a campaign against Allied shipping with the goal of cutting off Britain from the supplies needed to wage war. Overseen by Grand Admiral Erich 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 Karl 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, known as "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 (1939) and the Battle of the Denmark Strait (1941) 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 packs. These multi-ship groups were further directed by intelligence gleaned from the breaking of the British Naval Cypher No. 3. Armed with the approximate location of an approaching convoy, the wolf pack 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, the U-boats enjoyed tremendous success and inflicted heavy losses on Allied shipping. As a result, it became known as the "Happy Time" ("Die Glückliche Zeit") 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, SC 7, HX 79, and HX 90. In the course of the fighting, these convoys lost 11 of 43, 20 of 35, 12 of 49, and 11 of 41 ships respectively.

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

Guarding the Convoys

Though British destroyers and corvettes were equipped with ASDIC (sonar), the system was still unproven and was 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 United States via the Destroyers for Bases Agreement. In the spring of 1941, as British anti-submarine training improved and additional escort vessels reached the fleet, losses began to lessen and the Royal Navy began sinking 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 Franklin Roosevelt who extended the Pan-American Security Zone nearly to Iceland. Though neutral, the United States 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 US 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 American merchant ships as well as the US' failure to implement a coastal black-out.

As losses mounted, 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 continued to mount on both sides as the escorts and U-boats clashed. In November 1942, Admiral Sir Max Horton became commander-in-chief of the Western Approaches Command. As additional escort vessels became available, he formed separate forces which were tasked with supporting the convoy escorts. As they were not tied to defending a convoy, these groups were able to 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 Germany strategy of sinking ships faster than the 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. Though Allied losses dropped in April, the campaign pivoted on the defense of convoy ONS 5. Attacked by 30 U-boats it lost thirteen ships in exchange for six of Doenitz's boats.

Two weeks later, convoy SC 130 repelled German attacks and sunk five U-boats while taking no losses. The rapid turn in Allied fortunes was the result of the integration of several technologies which had become available in the preceding months. These included the Hedgehog anti-submarine mortar, continued advances in reading German radio traffic, enhanced radar, and the Leigh Light. 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." Combined with wartime ship construction programs, such as Liberty ships, these rapidly gave the Allies the upper hand. Dubbed "Black May" by the Germans, May 1943 saw Doenitz lose 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 new tactics and equipment. These included the creation of U-flak boats with enhanced anti-aircraft defenses as well as a variety of countermeasures and new torpedoes. Returning to the offensive in September, the U-boats enjoyed a brief period of success before Allied forces again began causing heavy losses. As Allied air power grew in strength, U-boats came under attack in the Bay of Biscay as they left and returned to port. With his fleet being reduced, Doenitz turned to new U-boat designs including the revolutionary Type XXI. Designed to operate entirely submerged, the Type XXI was faster than any of its predecessors. Only four were completed by the end of the war.


The final actions of the Battle of the Atlantic took place on May 7-8, 1945, just before the German surrender. In the course of the fighting, Allied losses totaled around 3,500 merchant ships and 175 warships, as well as around 72,000 sailors killed. German casualties numbered 783 U-boats and around 30,000 sailors (75% of the U-boat force). One of the most important fronts of the war, success in the Atlantic was critical for the Allied cause. Citing its importance, Prime Minister Winston Churchill later stated:

"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..."