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 Navy 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 in 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 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 ini­tial autho­ri­za­tion totaled $7 billion. By the end of the war U.S. expenditures would top $50 billion (equivalent to nearly $660 billion in 2015 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 shipBattle of the Atlantic: U.S. Navy flies antisubmarine patrol

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 millions of 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 attackBattle of the Atlantic: St. George's Ensign flies over U-boat

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 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