View source for Leigh Light

{{Short description|Submarine search light}}
{{Use dmy dates|date=December 2019}}
[[Image:Leigh Light.jpg|right|thumb|A Leigh Light fitted under the wing of a [[Consolidated B-24 Liberator|Consolidated Liberator]] aircraft of the Royal Air Force Coastal Command, 26 February 1944]]

The '''Leigh Light''' ('''L/L''') was a British [[World War II]] era [[anti-submarine warfare|anti-submarine device]] used in the [[Battle of the Atlantic]]. It was a powerful (22&nbsp;million [[candela]]s) [[Arc lamp#Carbon arc lamp|carbon arc]] [[searchlight]] of {{convert|24|in}} diameter fitted to a number of the British [[Royal Air Force]]'s [[RAF Coastal Command|Coastal Command]] [[patrol bomber]]s to help them spot surfaced [[Nazi Germany|German]] [[U-boat]]s at night.<ref>{{Cite web |url=http://www.rafb24.com/index.php?option=com_content&view=article&id=4643:leigh-light-operation&catid=29:the-b-24&Itemid=41 |archive-url=https://web.archive.org/web/20091111201629/http://www.rafb24.com/index.php?option=com_content&view=article&id=4643%3Aleigh-light-operation&catid=29%3Athe-b-24&Itemid=41 |url-status=dead |archive-date=11 November 2009 |title=Leigh Light Operation |author=Peter Clare |publisher=rafb24.com |date=22 July 2009}}</ref>

Early night operations with the new [[air-to-surface-vessel radar|air-to-surface-vessel (ASV) radar]] demonstrated that the radar's minimum range of about {{convert|1|km}} meant that the target was still invisible when it disappeared off the radar display. Efforts to reduce this minimum were not successful, so wing commander [[Humphrey de Verd Leigh]] hit upon the idea of using a searchlight that would be switched on just when the target was about to disappear on radar. The U-boat had insufficient time to dive and the bombardier had a clear view of the target. Introduced in June 1942, it was so successful that for a time German submarines were forced to switch to charging their batteries during the daytime, when they could at least see aircraft approaching.<ref name="Bowman2014">{{cite book |last=Bowman |first=Marin |title=Deep Sea Hunters: RAF Coastal Command and the War Against the U-Boats and the German Navy 1939–1945 |url=https://books.google.com/books?id=qGdtBQAAQBAJ&pg=PA61 |year=2014 |publisher=Pen and Sword |isbn=978-1-78383-196-8 |pages=61–79}}</ref>

Germany introduced the [[Metox]] [[radar warning receiver]] in an effort to counter the combination of ASV and Leigh Light. Metox provided the submarine crew with early warning that an aircraft using radar was approaching.<ref name="Owen2007">{{cite book |last=Owen |first=David |title=Anti-Submarine Warfare: An Illustrated History |url=https://books.google.com/books?id=W2GCAwAAQBAJ&pg=PA111 |year=2007 |publisher=Seaforth Publishing |isbn=978-1-78346-897-3 |page=111}}</ref> Because the radar warning receiver could detect radar emissions at a greater range than the radar could detect vessels, this often gave the U-boat enough time to dive. Having expected this, the Allies introduced the centimetric [[ASV Mk. III radar]], regaining control of the battle. Although the German [[Naxos radar detector|Naxos]] countered these radars, by this time the U-boat force was already damaged beyond repair.

==Development==
Early air-to-surface [[radar]] sets, namely the [[ASV Mk. II radar|ASV Mk. II]], had an inconveniently long minimum detection range. Thus as the aircraft approached the target, it would disappear off the radar at a range that was too great to allow it to be seen by eye at night without some form of illumination. At first, aircraft solved this problem by dropping flares to illuminate the area, but since the flare illuminated only the area directly beneath the aircraft, a series of flares in succession would have to be dropped until the submarine was spotted. Once it was spotted, the aircraft would circle back to attack, the entire process giving the submarine time to dive.

Eventually, time-delayed flares were developed that allowed the attacking plane time to circle. The flare was fired into the air from a buoy previously dropped by the plane. The surfaced submarine could then be seen in silhouette as the plane approached.

[[Wing Commander (rank)|Wing Commander]] [[Humphrey de Verd Leigh]], an RAF personnel officer, devised a solution after chatting with returning aircrew. This was to mount a searchlight under the aircraft, pointed forward and allowing the submarine to be spotted as soon as the light was turned on. He then developed the Leigh Light on his own, in secret and without official sanction—even the Air Ministry were unaware of its development until shown the completed prototype.<ref>''The Secret War'', by Brian Johnson, Pen And Sword Military Classics, 1978, {{ISBN|1-84415-102-6}}, pages 216–217.</ref> At first it was difficult to fit on aircraft due to its size. Leigh persisted in his efforts to test the idea and garnered the support of the Commander-in-Chief of Coastal Command, Sir [[Frederick Bowhill]]. In March 1941 a [[Vickers Wellington|Vickers Wellington DWI]] that conveniently already had the necessary generator on board (it had been used for anti-magnetic mining operations using a large electromagnet) was modified with a retractable "dustbin" holding the lamp and proved the concept sound.

At this point the [[Air Ministry]] decided that the idea was worthwhile, but that they should instead use the [[Turbinlite]], a less effective system which had been originally developed as an aid for night-time [[bomber]] interception. After trials they too eventually decided to use Leigh's system, but it was not until mid-1942 that aircraft started being modified to carry it. Development assistance and production was by Savage and Parsons Ltd. of Watford led by Jack Savage.<ref>[http://www.flightglobal.com/pdfarchive/view/1945/1945%20-%201929.html Death of Jack Savage], ''Flight'', 27 September 1945, page 350. Accessed October 2010.</ref>

==Operation==
[[Image:Destroyed U Boat illuminated in Leigh Lights.jpg|right|thumb|Photograph of a destroyed U-boat illuminated in Leigh Lights]]

Two types of Leigh Light entered operational use:<ref>{{cite web | url= http://www.rafb24.com/index.php/the-liberator/b-24indetail/4732-the-leigh-light-for-night-anti-submarine-operations | title= The Leigh Light For Night Anti-Submarine Operations | author= Peter Clare | publisher= RAF Liberator Squadrons, PC | date= 22 July 2009 | access-date= 14 August 2013}}</ref>

#The Turret type, fitted on Wellington aircraft, was a {{convert|24|in|adj=on}} searchlight mounted in a retractable under-turret controlled by hydraulic motor and ram. The maximum beam intensity was 50&nbsp;million candelas without the spreading lens and about 20&nbsp;million candelas with the lens. Total weight was {{cvt|1,100|lb}}.
#The Nacelle type, fitted on Catalinas and Liberators, was a {{convert|20|in|adj=on}} searchlight mounted in a nacelle {{convert|32|in}} in diameter slung from the bomb lugs on the wing. The controls were electric and the maximum beam intensity was 90&nbsp;million candelas without the spreading lens and about 17&nbsp;million with the lens. Total weight was {{cvt|870|lb}}.

By June 1942, aircraft equipped with ASV radar and the Leigh Light were operating over the [[Bay of Biscay]] intercepting U-boats moving to and from their home ports on the coast of France. The first submarine to be successfully sighted was the Italian submarine ''[[Italian submarine Luigi Torelli|Torelli]]'', on the night of 3 June 1942,<ref>{{cite book|last1=Giorgerini|first1=Giorgio|title=Uomini sul fondo : storia del sommergibilismo italiano dalle origini a oggi|date=2002|publisher=Mondadori|location=Milano|isbn=8804505370|pages=518–20}}</ref> and the first confirmed kill was the {{GS|U-502}}, sunk on 5 July 1942 by a Vickers Wellington of [[No. 172 Squadron RAF|172 Squadron]], piloted by American Wiley B. Howell. In the previous five months not one submarine had been sunk, and six aircraft had been lost. The Leigh Light turned the tables, and by August the U-boats preferred to take their chances in daytime when they had some warning and could fight back.

At least one [[Fairey Swordfish I]] biplane torpedo bomber was trialled with a Leigh Light under the lower port wing, with a large battery pack slung under the fuselage where the torpedo would normally be carried. The armament was a rack of anti-submarine bombs carried under the other wing. With such a heavy load performance was poor with a top speed marginally above the stall speed.<ref>Brown, Eric ''Wings on my Sleeve''</ref> A Swordfish III was also fitted with a Leigh Light under the starboard wing, at some point, although it is unclear where the battery pack was stowed as the ASV radar scanner apparently filled the torpedo area.<ref name=Taylor>{{cite book |last1=Taylor |first1=H.A. |title=Fairey aircraft since 1915 |date=1974 |publisher=Putnam |location=London |isbn=037000065X |pages=236–260 |edition=1st}}</ref>

[[Wing Commander (rank)|Wing Commander]] [[Peter Cundy]] was also given the [[Air Force Cross (United Kingdom)|Air Force Cross]] for his part in the development of the Leigh Light.

==Training==
[[Image:Putsborough Observation Post.jpg|right|thumb|The Observation Post at Putsborough overlooking Morte Bay]]
[[Image:Putsborough 1.jpg|right|thumb|The Indicator arrow at Putsborough overlooking Morte Bay]]

The observation post and concrete indicator arrow at [[Putsborough]] were built for Leigh Light training. A buoy anchored in [[Morte Bay]] was used as a target. Two other sites at [[Woolacombe]] and midway along the bay provided triangulation to assess the accuracy of the bombing attempt.<ref>{{cite web | url= http://historicengland.org.uk/listing/the-list/list-entry/1465902 | title = Second World War bombing range indicator and observation post | publisher = Historic England | date = 30 August 2019 | access-date = 4 October 2020}}</ref>

==Effectiveness==
Before the Leigh Light, not a single enemy submarine had been sunk in over five months, but in combination with radar, it was so overwhelmingly effective that many German submarine crews chose to surface during the day so that they could at least see the aircraft attacking them and have a chance to fire their anti-aircraft weaponry in defense.<ref>Giorgerini, Giorgio (2002). Uomini sul fondo : storia del sommergibilismo italiano dalle origini a oggi. Milano: Mondadori. pp. 518–20. {{ISBN|8804505370}}.</ref><ref>The Secret War, by Brian Johnson, Pen And Sword Military Classics, 1978, {{ISBN|1-84415-102-6}}</ref>

==References==
{{reflist}}

==External links==
{{Commons category|Leigh light}}
*[http://uboat.net/allies/technical/leigh_light.htm Technical details of the Leigh Light]

{{Uboat}}

{{DEFAULTSORT:Leigh Light}}
[[Category:Military aviation]]
[[Category:World War II military equipment of the United Kingdom]]
[[Category:Searchlights]]
[[Category:Military equipment introduced from 1940 to 1944]]