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The battle of the Atlantic infographic
Graphic charts the Battle of the Atlantic and features cut aways of the German U-Boat and torpedo.

The battle of the Atlantic

May 19, 1993 - The Battle of the Atlantic lasted just two days short of the duration of World War II. It cost the lives of 30,000 Allied merchant seamen and defensive gun crew and 20,000 German U-Boat crew.

Strategically, the battle for the North Atlantic - the campaign to destroy the convoys carrying vital supplies to Britain to sustain the war effort - can be divided into three phases. Phase one, August 1940 to December 1941, saw the German U-Boats enjoy undeniable superiority, decimating Allied merchant shipping in the waters off western Europe. Phase two, December 1941 to June 1942, saw the U.S. enter the war and the U-Boats switch their activities to the North American seaboard and the Caribbean, picking off shipping as easily as before. But phase three, June 1942 to May 1943, saw a combination of technological improvements, co-operation between the Allied powers and all branches of the armed forces finally dominate the diesel-electric submarine.

At the outbreak of hostilities neither the British nor the German Navy was well equipped for combat and the first two years of the war saw both sides hastily devising measure and countermeasure to achieve naval superiority. Germany achieved early success with their magnetic mine, dropped by air into the shallow coastal waters around Britain. By late 1939, these accounted for 59 merchant shipping casualties as opposed to 47 sunk by U-Boats but their usefulness was negated after an intact mine was retrieved from mud flats and its construction discovered.

The development of sonar allowed British ships to locate the U-Boats but lack of trained operators and the difficulties of equipping ships quickly enough brought only limited success.

With the capture of a British submarine in May 1940, German designers discovered that torpedo tubes could be made from steel as opposed to cast in bronze, which enabled them to build submarines at a much faster rate. By September 1940, U-Boat numbers were restored to 57, the same as the first day of the war. Increasing numbers meant that the German Navy, under Admiral Dönitz, was able to introduce the “wolf-pack” tactic, whereby once a U-Boat had located a convoy all available submarines in the vicinity gathered to attack - by night and from the surface, where not only were they barely visible, but sonar was unable to detect them.

The British Navy was boosted by Norwegian, Belgian, Dutch and French ships seeking refuge from German occupation of home territory but U-Boat domination remained unassailable. In October 1940, 63 Allied or neutral merchant vessels (352,407 tons) were sunk, 56 of them in the North Atlantic. That month U-Boats sank an average daily total of 920 tons - unequalled at any other stage of the battle. With the Atlantic convoys and their naval escorts seemingly able to be picked off at will, rationing bit hard in beleaguered Britain.

In 1941, three developments gave the advantage back to the Allies. Type 271 radar could locate a U-Boat conning tower, thus elimimating the surface advantage. This was followed by “Huff-Duff” (HF/DF) - High Frequency Direction Finding - which allowed the sub’s position to be plotted at speed, and then by radar fitted to aircraft which, when coupled with a powerful search light under the wing, made escape almost impossible. Germany countered with the Biscay Cross, a radar detector which warned the U-Boat commander that radar was locked on to him.

Once the U.S. had joined the war their shipping swelled the Atlantic fleet and the advent of the radio telephone permitted communication between ships. By March 1943 further radar developments, more sophisticated depth charges and scatter weapons, which confused the U-Boats as to the postition of their enemy, redressed the balance yet again. Long-range air cover provided protection for ships in mid-Atlantic and, with American and British shipbuilders working round the clock to build new ships and repair damaged ones, construction outnumbered losses for the first time.

But above all, it was the cracking of the Enigma code that permitted the Allies to divert convoys around the wolfpacks and inflict devasting losses on the U-Boats during April and May 1943. British attempts to intercept the succession of coded messages relayed to U-Boat commanders from Dönitz’s headquarters during the early years of the war had failed but following the 1941 capture of a U-Boat with its Enigma machine intact, a succession of mathematicians, linguists, chess and crossword puzzle experts based at Bletchley Park finally broke the mind-mangling permutations of the code.

U-Boats had sunk five million tons of shipping in 1942 but by May 1993 losses were reduced to a trickle and by the end of the year continued Allied production enabled a massive offensive capability, without which the invasion of Normandy in June 1944 could not have taken place.
The Battle of the Atlantic claimed vast numbers, of human lives and of shipping. Of 4,786 Allied ships lost worldwide during the war, 2003 were lost to submarine attack in the North Atlantic, as opposed to only 310 sunk by surface raiders, aircraft and mines. A further 1,000 were damaged but managed to limp to a friendly port for repair. Of 1089 U-Boats built, 420 were destroyed in or en route to the North Atlantic, with a further 60 in British waters.

As a weapon of war, the power of the U-Boat was immense. The turning point may have come in May 1943, but the Battle of the Atlantic continued a further two years - the longest campaign of the war.

PUBLISHED: 19/5/1993; STORY: Julie Hacking