The Crucial Battle of the Atlantic During World War II
The Crucial Battle of the Atlantic During World War II

The Crucial Battle of the Atlantic During World War II

Larry Holzwarth - January 17, 2020

The Crucial Battle of the Atlantic During World War II
Crewmen from HMS Petard recovered TRITON code documents, but their attempt to capture an Enigma machine cost them their lives. Wikimedia

21. Codebreakers contributed to the Allied effectiveness throughout much of the battle

The story of the Polish and British cracking of the German codes processed through Enigma machines is far too extensive for inclusion here. What is pertinent is the German Navy’s use of an Enigma-based code called TRITON beginning in 1942. USS TRITON used the four-wheel version of the Enigma system. The change to TRITON temporarily left the British codebreakers in the dark. In late October, 1942, a German U-boat was attacked by HMS Petard in the Mediterranean. In company with other British destroyers, Petard forced the U-boat to the surface, and its crew abandoned the ship near Port Said. A team from Petard boarded the sinking submarine.

A complete four-wheel Enigma machine and some TRITON code books and documents were left behind by the Germans. The British were able to capture the code books and return them to Petard. The submarine sank quickly, taking the Enigma and two British seamen who attempted to extract it to the bottom. With the information recovered by Petard, the British were able to crack the remainder of the TRITON code, and were made aware of the operations controlled by Doenitz. It allowed the British and Americans to be ready and waiting when the U-boats made an appearance.

The Crucial Battle of the Atlantic During World War II
Survivors from a sunken U-boat awaiting rescue by an Allied ship. Imperial War Museum

22. The code breakers were blinded again in early 1943

In early 1943, the number of U-boats operating in the Atlantic again threatened to overwhelm the convoy escorts, in part because the Germans made changes to TRITON. For over a week, the British codebreakers at Bletchley Park had no information about Doenitz’s plans. In March, 1943, over 475,000 tons of Allied shipping went down in the Atlantic, in 82 ships. In the Indian Ocean, the Caribbean, and the Pacific, another 38 ships were lost to U-boats. The Allies destroyed 12 German submarines in return.

The following month the tide turned against the Germans. U-boat losses mounted. Through April the Germans sank 39 Allied ships, totaling 235,000 tons. But many more ships got through, resupplying the nearly desperate British. 15 U-boats were lost as the Allies refined their tactics using newly developed weapons. The American shipbuilding program produced more and more destroyer escorts and destroyers, as well as long-range bombers and flying boats. Escort carriers surrounded by a task force developed specifically for anti-submarine warfare actively hunted the Germans.

The Crucial Battle of the Atlantic During World War II
The escorted convoy system led to the defeat of the U-boat threat by early 1944. Wikimedia

23. Black May broke the back of the German U-boat fleet

May, 1943, was the month in which the Allied Navies effectively defeated the U-boat threat. At the end of April and through the first week of May, a slow convoy of 43 ships and seven escorts was attacked by more than 30 U-boats. The allies lost 13 ships to the U-boat attacks which continued for week, but most of the attacks were unsuccessful. The combination of aerial observation and attack, depth charges, hedgehogs, and surface gunfire proved deadly for the Germans. The 13 ships sunk (63,000 tons) cost Doenitz 6 U-boats, with another 7 returned to port too damaged to rejoin the fight for some time.

During the month of May, in all actions, 43 U-boats were destroyed, 34 of them in the Atlantic. The same number of Allied ships were lost in the Atlantic, 34 ships. It was a loss of 135,000 tons, but it cost the Germans a full quarter of the available U-boat fleet. Doenitz withdrew his remaining boats from the North Atlantic, accepting defeat. German U-boat activity continued through the remainder of the war, but the concerted effort to defeat Great Britain by choking off its supplies was over. The Allies did not yet know it, but they had won the Battle of the Atlantic.

The Crucial Battle of the Atlantic During World War II
German prisoners from U-873 arrived at Portsmouth, New Hampshire, in 1945. US Navy

24. The U-boats were driven out of the South Atlantic the same year

The defense of the convoys in the South Atlantic was coordinated by the United States Navy and the small but effective Brazilian Navy and Air Force. The Brazilians escorted more than 600 convoys during the war, with a loss rate of 0.1%. More than 16,000,000 tons of supplies and equipment reached their destination safely under Brazilian escort, though submarine attacks by the Germans and Italians were common. American and Brazilian long-range aircraft, mostly B-24 Liberators, attacked enemy U-boats and reported their positions to surface ships which drove them off or destroyed them.

The Italians and the Germans both lost submarines in the waters patrolled by the Brazilians, who had entered the war partly in response to U-boats’ sinking ships off their coast. Between January and September 1943, German U-boats were sunk at a rate of more than one per month in Brazilian waters. For the Germans, they were irreplaceable by that stage of the war. The Allied bombing of German industries made construction of newer and more effective submarines difficult. In September, 1943, Doenitz launched a final attempt to defeat the Allies in the North Atlantic with U-boats. They sank 14 Allied ships (six of them warships) at a cost of 39 U-boats.

The Crucial Battle of the Atlantic During World War II
A war poster encouraging production for suppliers of the shipbuilding industry. National Archives

25. The costs of the Battle of the Atlantic were staggering

German U-boat activity continued through the end of the war, but the Battle of the Atlantic was won by January, 1944. When the war ended and the remainder of the U-boat fleet surrendered, the total was added up. 783 U-boats were destroyed (or captured) and 30,000 German sailors killed, 75% of the total U-boat fleet personnel. Germany also lost 4 battleships, 9 cruisers, and more than two dozen destroyers. The Germans sank 175 Allied warships. The damage inflicted on the Allies’ merchant fleets was brutal. Over 6,000 Allied freighters and tankers were lost. They took with them the lives of more than 72,000 seamen. Over 36,000 of them were civilian merchant seamen from all over the world.

Had the Allies not prevailed in the Battle of the Atlantic, the great buildup of arms and men in Great Britain for Operation Overlord could not have been achieved. The total losses in terms of tonnage was over 21 million tons, all of it sent to the bottom of the ocean, where most of it remains. The ships were replaced by over 38 million tons of new shipping, most of which was built in the United States, at enormous costs. Though historians dispute how close Germany came to winning the Battle of the Atlantic, there is little dispute over its cost in lives and materiel for all of the contending nations.


Where do we find this stuff? Here are our sources:

“Escort of Convoy: Still the Only Way”. R. A. Bowling, Proceedings, United States Naval Institute. December, 1969

“Battle of the Atlantic”. Bernard Ireland. 2003

“The Battle of the Atlantic”. Donald Macintyre. 1961

“The Atlantic Campaign”. Dan van der Vat. 1988

“Ten Years and Twenty Days”. Karl Doenitz. 1959

“Wolf Packs”. Ivano Massari, War History Online. April 25, 2018

“The Italian Submarine Base in Bordeaux, France”. Christiano D’Adamo. Regia Marina Italiana. Online

“The Nazi Marauder”. Jon Guttman, History Net. Online

“Escort: The Battle of the Atlantic”. D. A. Rayner.

“Visiting Bismarck: Explorers Revise Its Story”. William J. Broad, The New York Times. December 3, 2002

“Battleship Bismarck: A Survivor’s Story”. Burkhard von Müllenheim-Rechberg. 1980

“The Real Cruel Sea: The Merchant Navy in the Battle of the Atlantic”. Richard Woodman. 2004

“U-boat Assault on America: Why the US was Unprepared for War in the Atlantic”. Ken Brown, US Naval Institute.

“The Defeat of the German U-boats: The Battle of the Atlantic”. David Syrett. 1994

“Business in Great Waters”. John Terraine.1987

“The Brazilian Navy in World War II”. Homer C. Votaw. 1950

“The Battle of the Atlantic”. Samuel Eliot Morison. 1947

“Galloping Ghosts of the Brazilian Coast”. Alan C. Carey. 2004

“All Hell Let Loose: The World at War, 1939-1945”. Max Hastings. 2012