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 $678 billion in 2017 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 date Battle 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.

Battle of the Atlantic: U-848 under attack, November 5, 1943 Battle 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. By the end of 1943, how­ever, the Allies had begun to 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