page_title: Battle of the Atlantic
section_title: Leigh Light
hierarchical_section_title: Battle of the Atlantic / Battle returns to the mid-Atlantic (July 1942 – February 1943) / Leigh Light
caption_attribution_description: English: Anti-Submarine Weapons: Leigh Light used for spotting U-boats on the surface at night fitted to a Liberator aircraft of Royal Air Force Coastal Command.
context_page_description: The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the Naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. The campaign peaked from mid-1940 through to the end of 1943.
  The Battle of the Atlantic pitted U-boats and other warships of the German Kriegsmarine and aircraft of the Luftwaffe against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. Convoys, coming mainly from North America and predominantly going to the United Kingdom and the Soviet Union, were protected for the most part by the British and Canadian navies and air forces. These forces were aided by ships and aircraft of the United States beginning September 13, 1941. The Germans were joined by submarines of the Italian Regia Marina after Germany's Axis ally Italy entered the war on June 10, 1940.
  As a small island country, the United Kingdom was highly dependent on imported goods.
context_section_description: Detection by radar-equipped aircraft could suppress U-boat activity over a wide area, but an aircraft attack could only be successful with good visibility. U-boats were relatively safe from aircraft at night for two reasons: 1) radar then in use could not detect them at less than 1 mile (1.6 km); 2) flares deployed to illuminate any attack gave adequate warning for evasive manoeuvres. The introduction of the Leigh Light by the British in January 1942 solved the second problem, thereby becoming a significant factor in the Battle for the Atlantic. Developed by RAF officer H. Leigh, it was a powerful and controllable searchlight mounted primarily to Wellington bombers and B-24 Liberators. These aircraft first made contact with enemy submarines using air-to-surface-vessel (ASV) radar. Then, about a 1 mile (1.6 km) from the target, the Leigh light would be switched on. It immediately and accurately illuminated the enemy, giving U-boat commanders less than 25 seconds to react before they were attacked with depth charges. The first confirmed kill using this technology was U-502 on July 5, 1942.
  The Leigh light enabled the British to attack enemy subs on the surface at night, forcing German and Italian commanders to remain underwater especially when coming into port at sub bases in the Bay of Biscay. U-boat commanders who survived such attacks reported a particular fear of this weapon system since aircraft could not be seen at night, and the noise of an approaching aircraft was inaudible above the din of the sub's engines. Subsequently, the common practice of surfacing at night to recharge batteries and refresh air was mostly abandoned as it was safer to perform these tasks during daylight hours when enemy planes could be spotted. A drop in Allied shipping losses from 600,000 to 200,000 tons per month was attributed to this device.
caption: Leigh Light fitted to a Royal Air Force Coastal Command Liberator, February 26, 1944
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