Battle of the Atlantic
From June until October 1940, over two hundred seventy Allied ships were sunk by German U-boats operating from newly captured French bases. This period became known as the Happy Time among U-boat crews who viewed themselves as heroes. Günther Prien of U-47, Otto Kretschmer, Joachim Schepke, Engelbert Endrass, Victor Oehrn, and Heinrich Bleichrodt led spectacular operations. The biggest challenge for these commanders was finding convoys in the vast ocean. Focke-Wulf Fw 200 Condor aircraft based at Bordeaux and Stavanger provided reconnaissance using converted civilian airliners. Codebreakers at Bletchley Park deciphered British Naval Cypher No. 3 allowing Germans to estimate convoy locations. Instead of attacking single targets, U-boats worked in wolf packs coordinated by radio. A patrol line of boats would search for a convoy then converge to attack together at night from the surface. When one boat sighted a convoy it reported the sighting to headquarters while shadowing the target. Other boats arrived typically at night to face groups of up to half a dozen submarines simultaneously. On September twenty-first, four U-boats attacked Convoy HX 72 sinking eleven ships and damaging two over two nights. In October, slow Convoy SC 7 lost fifty-nine percent of its ships despite an escort of two sloops and two corvettes. The battle for HX 79 proved even worse for escorts losing a quarter of their convoy without any loss to U-boats. At year end, seven German and three Italian submarines caught HX 90 sinking ten ships and damaging three others.
High-frequency direction-finding equipment known as HF/DF started fitting onto escorts from February 1942. These sets allowed operators to determine signal direction regardless of content readability since wolf packs relied on radio reports. An escort could run toward the signal or force the submarine to submerge causing loss of contact. Two sets enabled position fixes rather than just bearings eliminating the need for triangulation. British codebreakers at Bletchley Park used captured Enigma rotors from U-110 in May 1941 to read all U-boat traffic for several weeks. A reverse-engineered machine programmed with suggested settings decrypted messages until keys ran out. Throughout late 1941, Enigma intercepts combined with HF/DF enabled plotting patrol lines routing convoys around them. Merchant ship losses dropped by over two-thirds in July 1941 remaining low until November. The Type VIIC began reaching Atlantic numbers in large quantities by 1941 with five hundred sixty-eight commissioned by war's end. Coastal Command Hudson aircraft captured U-570 south of Iceland on August twenty-seventh 1941. Squadron Leader J. Thompson sighted the surfaced submarine diving immediately and releasing four depth charges. The crew displayed a white flag allowing the vessel to be beached in an Icelandic cove without recovering codes. This complete U-boat was later commissioned into the Royal Navy as HMS Graph.
On July nineteenth 1942 Dönitz ordered U-boats withdrawn from American waters shifting focus back to North Atlantic where Allied aircraft could not provide cover. This region became known as the Black Pit or air gap between Greenland and Iceland. Convoy SC 94 marked the return of U-boats to routes from Canada to Britain. Command centers moved to Château de Pignerolle east of Angers on the Loire river under Hans-Rudolf Rösing. Often ten to fifteen boats attacked multiple convoy routes following ships like SC 104 and SC 107 by day then striking at night. In October 1942, fifty-six ships totaling over two hundred fifty-eight thousand tons were sunk within this air gap. U-boat losses climbed significantly with sixty-six destroyed in the last six months of 1942 compared to twenty-one lost earlier that year. Admiral Max Horton replaced Admiral Noble as Commander-in-Chief Western Approaches Command on November nineteenth 1942. He organized support groups reinforcing convoys under attack rather than staying directly responsible for safety. Captain John Walker introduced hold-down tactics patrolling submerged submarines until air ran out forcing surfacing after days. By spring 1943, so many U-boats patrolled difficult evasion resulting in succession of vicious battles.
March 1943 saw one hundred twenty ships sunk worldwide including eighty-two vessels totaling four hundred seventy-six thousand tons in Atlantic waters while twelve U-boats were destroyed. British supply situations became critical fuel shortages prompting consideration abandoning convoins entirely. April brought complete reversal fortunes with only thirty-nine ships totaling two hundred thirty-five thousand tons sunk and fifteen U-boats destroyed. By May wolf packs no longer held advantage making it known as Black May in the U-boat Arm. The turning point centered on slow Convoy ONS 5 comprising forty-three merchantmen escorted by sixteen warships attacked by a pack. Allied technological countermeasures neutralized submarine threats decisively during this period. Hedgehog ahead-throwing mortars fired contact-fused bombs exploding only upon direct hit preventing disturbed water complicate tracking. Squid improved Hedgehog design projecting charges automatically linked to latest ASDIC sets. Leigh Lights mounted on Wellington bombers illuminated surfaced submarines giving commanders less than twenty-five seconds reaction time before depth charge attacks. First confirmed kill using this technology occurred July fifth 1942 against U-502. Metox radar detectors fitted to U-boats allowed avoidance of ambushes but failed when British changed radar pulse frequencies doubling beeping warning range.
Hedgehog anti-submarine mortars started installing on ships from late 1942 firing contact-fused bombs ahead while target remained within ASDIC beam. Warships approached slowly reducing noise making position less obvious to submarine commanders. Because weapons exploded only on impact missed targets left undisturbed water allowing continued tracking. Squid introduced late 1943 projected charges automatically set pistols just before launch linking directly to advanced ASDIC sets. Leigh Lights developed by RAF officer H. Leigh mounted powerful searchlights primarily on Wellington bombers and B-24 Liberators. Aircraft located enemy submarines using air-to-surface-vessel radar then switched lights on about nine miles away illuminating targets accurately. U-boat commanders reported particular fear since aircraft remained invisible at night with engine noise inaudible above sub sounds. Common practice surfacing nightly recharging batteries abandoned as safer daylight operations allowed spotting planes. Metox receivers enabled avoiding detection by metric radar bands used early radars causing problems sometimes detecting stray emissions preventing unnecessary submerging. Germans broke Admiralty codes March 1942 reading eighty percent of messages until June 1943 increasing merchant ship sinkings dramatically. Günter Hessler stated one or two days required decrypting British radio messages enabling closing gaps before convoys arrived.
Britain required more than one million tons imported material weekly surviving fighting war. The Battle involved tonnage war where Allies struggled supplying Britain while Axis targeted merchant shipping critical to effort. Rationing reduced demand reducing wastage increasing domestic production equality distribution. From 1942 onwards Axis sought preventing build-up Allied supplies equipment UK preparation invasion occupied Europe. Defeat U-boat threat prerequisite pushing back Axis western Europe outcome strategic victory Allies German tonnage war failed great cost three thousand five hundred merchant ships and one hundred seventy-five warships sunk Atlantic loss seven hundred eighty-three U-boats forty-seven German surface warships including four battleships nine cruisers seven raiders twenty-seven destroyers. Germany spent more money producing naval vessels every type ground vehicle combined tanks according United States Strategic Bombing Survey Vol 3 Effects Strategic Bombing German War Economy 1945 page 144. Winston Churchill wrote only thing frightened him during war was U-boat peril even more anxious battle called Battle of Britain. First Lord Admiralty A.V. Alexander asked Parliament March fifth 1941 many more ships great numbers men fight Battle Atlantic compared Battle France fought previous summer.
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Common questions
How many German U-boats were available in September 1939?
The German U-boat fleet numbered only fifty-seven vessels in September 1939. Most of these boats were small Type II designs intended for coastal minelaying rather than deep ocean warfare.
When did the Battle of the Atlantic turn against Germany in May 1943?
May 1943 became known as Black May when wolf packs lost their advantage and suffered heavy losses. During this month, one hundred twenty ships were sunk worldwide while twelve U-boats were destroyed by Allied countermeasures.
What equipment allowed British escorts to detect U-boat radio signals from February 1942?
High-frequency direction-finding equipment known as HF/DF started fitting onto escorts from February 1942. These sets enabled operators to determine signal direction regardless of content readability since wolf packs relied on radio reports.
Why was the region between Greenland and Iceland called the Black Pit during World War II?
This area became known as the Black Pit or air gap because Allied aircraft could not provide cover over those waters. On July nineteenth 1942 Dönitz ordered U-boats withdrawn from American waters shifting focus back to North Atlantic where this lack of air support existed.
How many merchant ships were lost during the entire Battle of the Atlantic?
The Atlantic loss included three thousand five hundred merchant ships and one hundred seventy-five warships sunk. German tonnage war failed at great cost with four battleships nine cruisers seven raiders and twenty-seven destroyers also lost alongside the submarines.