London, England March 6, 1941

By January 1941 the Allies had lost 1,300 merchant ves­sels, almost half of them to German U‑boats. Following the enslave­ment of 120 mil­lion peo­ple in seven West­ern and East­ern Euro­pean coun­tries by Nazi Ger­many the pre­vious year, the British were reduced to fighting Adolf Hitler’s mili­tary jugger­naut alone. In alarm they watched the sharp re­duc­tion of their food sup­plies and war mate­rial from the U.S. and Canada as the German Kriegs­marine and, to a smaller extent, the Luft­waffe sent mer­chant­man after mer­chant­man to the bottom of the ocean. As an island nation, the British were highly depen­dent on im­ported goods, requiring more than a million tons of imported material per week just to survive and fight.

Using the example of the 1940 Battle of Britain, in which the Royal Air Force held Her­mann Goering’s Luft­waffe at bay from July to October 1940, Brit­ish Prime Minis­ter Winston Chur­chill pro­claimed the Battle of the Atlan­tic on this date, March 6, 1941. (The battle would turn out to be the longest contin­uous mili­tary cam­paign of the Euro­pean war.) The next four months, Chur­chill pre­dicted, would be used to defeat the Kriegs­marine’s attempt to sever the naval connec­tion between North America and Britain. Four days later, Pre­si­dent Franklin D. Roose­velt threw Britain a life­line in the form of the Lend-Lease Act. Though the U.S. would not be pulled into war for nine more months, the hall­mark legis­lation, after vocif­erous debate in Congress, over­turned three suc­ces­sive Neu­trality Acts from the 1930s aimed at keeping the U.S. out of the Euro­pean conflict. Lend-Lease gave the Roose­velt admin­is­tra­tion legal autho­rity to send mili­tary and eco­nomic aid to coun­tries whose defense was deemed vital to the U.S. (The pres­i­dent used the months following the Act’s passage to autho­rize clan­des­tine meetings between U.S. and British mili­tary staffers.) The ini­tial autho­ri­za­tion of aid totaled $7 billion. By the end of the war U.S. expenditures would top $50 billion (equivalent to over $917 billion in 2020 dollars).

The first Lend-Lease food shipments left the U.S. on April 16, 1941, and helped avert an acute food short­age in Britain. Between April and Decem­ber 1941, the U.S. delivered one million tons of food to Britain. The assis­tance the U.S. gave its Allies in the early part of the war greatly helped revive the U.S. eco­nomy from the effects of the Great Depres­sion and placed it on a firm footing to enable it to join the fight against the Axis powers. When unleashed, the almost limit­less power of the U.S. agri­cul­tural and in­dus­trial econ­omy provided one of the principal weapons in the Allied victory.

Battle of the Atlantic: The Nazi Effort to Starve Britain into Surrender and the Allies’ Response

Battle of the Atlantic: U-boat shells merchant ship, unknown dateBattle of the Atlantic: U.S. Navy flies antisubmarine patrol, November 27, 1941

Left: A U-boat shells a merchant ship that remained afloat after being tor­pedoed. The Battle of the Atlantic was chiefly a ton­nage war—the Allies even­tually winning the struggle to supply Great Britain with food, arma­ments, and other neces­sities, while the Axis attempted to inter­dict mer­chant shipping that enabled the island nation to keep fighting. Lasting from 1939 to Germany’s capitu­la­tion in May 1945, the battle involved thou­sands of ships in more than 100 con­voy battles and upwards of 1,000 single-ship encounters, all taking place in a watery theater covering over 41 million square miles.

Right: A Vought SB2U Vindicator scout bomber from the USS Ranger flies anti­sub­marine patrol over a con­voy of mer­chant­men en route to Cape Town, South Africa, Novem­ber 27, 1941. The con­voy was one of many es­corted by the U.S. Navy on “Neu­tral­ity Patrol” before the country officially entered the war against the Axis on Decem­ber 8 (Japan) and 11 (Germany and Italy), 1941. Over time air­craft were the war-winning weapon in the Battle of the Atlantic. Long-range patrol planes and escort carrier air­craft even­tually closed the mid-Atlantic gap and made success­ful U-boat patrols an increasing rarity from mid-1943 on.

Battle of the Atlantic: U-848 under attack, November 5, 1943Battle of the Atlantic: St. George’s Ensign flies over U-boat, June 1945

Left: German submarine U-848 under attack in the South Atlantic, Novem­ber 5, 1943. Chur­chill wrote in his me­moirs, “The only thing that ever really frightened me during the war was the U‑boat peril.” There was a period during the winter of 1942–1943 when the Kriegs­marine came close to cutting the North Atlantic life­line. In the first 20 days of March 1943, the Germans sank 97 Allied mer­chant ships—twice the rate of replace­ment. How­ever, in that same month the Allies destroyed 43 U‑boats, or 25 per­cent of the Kriegs­marine’s entire oper­a­tional sub­marine strength. Grand Adm. Karl Doenitz briefly with­drew his U‑boats from the main convoy routes and abruptly ended what U‑boat crews had referred to as the “Happy Times” (die glueckliche Zeit). By the end of 1943, after another 39 U‑boats had been dispatched to the bottom of the ocean, the col­lective effects of the counter­mea­sures the Allies were employing had largely over­come the threat to their convoys crossing the Atlantic.

Right: Canadian seamen raise St. George’s Ensign above a German sub­marine in St. John’s har­bor, New­found­land, in June 1945. Both the Allies and the Ger­mans paid dearly in battling for con­trol of the Atlantic sea lanes. Between 1939 and 1945, 3,500 Allied mer­chant ships (totaling 14.5 mil­lion gross tons) and 175 Allied war­ships were sunk and some 72,200 Allied sailors, naval gunners, and mer­chant sea­men lost their lives. The Germans lost 783 U‑boats and roughly three-quarters of their 40,000‑man U‑boat fleet.

Nazi U-Boats Go After Trans-Atlantic Shipping While Allies Search for Counter­measures in the Battle for the Atlantic