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 in 1940, 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. In four months in 1940, from June to Septem­ber, U‑boats sank 274 ships for a loss of only two German sub­marines. The monthly aver­age of Allied mer­chant ships sunk jumped from the pre-June 1940 count of 60 per month to 98 per month. 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. In Febru­ary 1941 alone U‑boats, air­craft, and mines had destroyed 400,000 tons of shipping, and the rate had been increasing from one month to the next. Losses per trans­atlantic con­voy—escorted by Anglo-Cana­dian war­ships—were running at roughly 10 per­cent. Ship losses were two to three times larger than the rate at which Britain could build replace­ments. It was a bleak portrait indeed.

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 offi­cially pro­claimed the Battle of the Atlan­tic on this date, March 6, 1941. (The battle, waged across a great expanse of unfor­giving ocean and touching three con­ti­nents, would turn out to be argu­ably the most ardu­ous and 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 sea-lanes 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 cau­tious Roose­velt admin­is­tra­tion legal autho­rity to send much-needed 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 $838.4 billion in 2023 dollars adjusted for inflation).

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 U.S. oil tanker off Florida, 7-15-42Battle of the Atlantic: U.S. Navy flies antisubmarine patrol, November 27, 1941

Left: U-boats prowled the U.S. coast early in the war, and on July 15, 1942, the SS Penn­syl­vania Sun carrying 107,500 barrels of pre­cious Navy fuel oil fell victim to U571 125 miles (201 km) west of Key West, Florida, en route from to Port Arthur, Texas, to Belfast, Ireland. The Battle of the Atlantic was chiefly a ton­nage war—the Allies even­tually winning the struggle to supply Great Bri­tain with food and other agri­cul­tural pro­ducts, steel, oil, arma­ments, and other key neces­si­ties, while the Axis attempted to inter­dict mer­chant shipping that enabled the island nation to keep fighting instead of suing for peace. 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, America’s first purpose-build air­craft carrier launched in 1933, 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.” “The Battle of the Atlan­tic was the denomi­na­ting factor all through the war. . .  [E]very­thing happening else­where, on land, at sea or in the air, depended ulti­mately on its ou­tcome.” There was a period during the winter of 1942–1943 when the U‑boat branch of the Kriegs­marine came close to cutting the North Atlantic life­line. (The German sur­face fleet was never a serious factor in the Battle of the Atlan­tic.) 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 and a further 54 lost in the first three months of 1944, the col­lective effects of the counter­mea­sures the Allies were employing (e.g., acous­tic under­water detec­tion systems, air-to-surface radar in com­bi­na­tion with power­ful aircraft-mounted search­lights and anti­sub­marine bombs, Hedge­hog and Squid depth charges, increased air patrols over the full length of the convoy routes, and rerouting con­voys away from areas where U‑boats were oper­ating) had largely over­come the threat to their merchant­men 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 Transatlantic Shipping While Allies Search for Counter­measures in the Battle for the Atlantic