Monday, March 9, 2015

Battle of Britain – Electronic War

This Chain Home radar antenna, mounted on a 185- foot tower, was a central part of the Royal Air Force’s technological defense against the German air attack in the Battle of Britain. Multiple similar radar facilities were tied to RAF central command by telephone links enabling rapid fighter defense response to oncoming German aircraft.

The aerial Battle of Britain turned back a threatened German invasion in the fall of 1940. In addition to the aircraft, two integrated technologies played a large part— radar and the effective use of radio and ground telephone links. The British Royal Air Force (RAF) system of command and control made the difference in what some termed the “narrow margin” of victory.

Initially developed in the 1930s by Robert Watson-Watt and others, the first radar station was operational by 1937. By 1940, the RAF had in place fourteen Chain Home radio direction finding (RDF) stations, most equipped with four 350-foot transmitting towers holding a curtain aerial array. Incoming attacking aircraft could be located 100 miles away up to a height of 10,000 feet. Information about incoming German air raids from the Chain Home stations as well as ground observer reports were transferred to Fighter Command headquarters at Bentley Priory and to British fighter squadrons sent up to do battle. Low-flying aircraft could sometimes get in underneath the radar curtain until “low” RDF stations were added to the network.

The radar system was but one part of the extensive RAF control network that made British victory possible. Large regions of the country were assigned to groups that were subdivided into sectors. Local control rooms were linked by telephone to group and Fighter Command group headquarters in Uxbridge, west of London. A filter room would take in all the information (which after April 1940 could include Ultra decodes of German Luftwaffe signals), which was organized for display on large table maps with both British squadrons and German air fleets assigned codes. British aircraft carried “pip-squeak” radar that allowed their positions to be plotted from the ground.

They also carried a secret identification, friend or foe device, code named “Parrot,” so ground controllers could tell British from German fighters. The instruction to switch it on was therefore “Squawk your Parrot” (that term is still used today as modern transponder codes are known as “squawks”). Antiaircraft guns and searchlights were an integrated part of the system. Night fighting became possible with airborne ground control interception radar in November 1940, which, along with special training, allowed British fighter units to take on attacking German aircraft.

The Germans soon caught up with radar of their own. They also used a special radio navigational system called “crooked leg” (knickebein), first used in August–September 1940. This was a blind-bombing system that utilized radio direction to assist aerial navigation. Operating on 30 MHz, it was based on the Lorenz blind-landing system that had been pioneered in the 1930s. Pilots flew along one beam, dropping their bombs when they crossed a second beam. The British developed means of locating the two knickebein transmitters in France and either jammed their signals or knocked them out from the air.

Luftwaffe signals security was markedly lax (compared to the German army and navy) and Luftwaffe Enigma codes were among the first broken (April 1940) by British code breakers at Bletchley Park. By June intercepted messages provided the first information on the knickebein air navigation system.

Between the wars, the RAF was dramatically scaled down in equipment and personnel, only beginning to rebuild in the late 1930s. Technical development was also slowed, save for the innovation of radar on the eve of World War II. On Britain’s entry into the war on 3 September 1939, only one of 135 RAF squadrons was devoted to communications. It became the RAF Signals Organization, and much of its emphasis was on the vital radar technology.

On 1 January 1940 the RAF introduced identification, friend or foe (IFF) signals to help identify bomber, coastal, and fighter aircraft on radar screens. Radio likewise played a central role in the Battle of Britain. On 7 October 1940, No. 80 (Signals) Wing became the RAF’s first electronic warfare unit. As an example of what could be accomplished, on 13–14 November 1940, two aircraft of the Wireless Intelligence and Development Unit made the first direct attack on enemy navigational radar installations on the Cherbourg Peninsula by homing in on their transmission signals.

The RAF developed an extensive teleprinter network linking its ground control and airfield facilities. Communications hubs for these and voice communications were located in several underground centers around the country, interconnected by coaxial cable and high-frequency radio links. Links to aircraft included both voice (for fighters) and telegraphy (more for transports and bombers), both using code systems for security.

In his soon-to-be-immortal words about the British fighter pilots, British Prime Minister Winston Churchill told the House of Commons early in the battle (20 August 1940) that “Never in the field of human conflict was so much owed by so many to so few.”

Sources Dempster, Derek, and Derek Wood. 1961. The Narrow Margin: The Battle of Britain and the Rise of Air Power 1930–1940. New York: McGraw-Hill. His Majesty’s Stationery Office. 1941. The Battle of Britain: An Air Ministry Account of the Great Days from 8th August–31st October 1940. London: HMSO. Overy, Richard. 2002. The Battle of Britain: The Myth and the Reality. New York: Norton. Royal Air Force Museum. 1990. Against the Odds: The Battle of Britain Experience. London: Royal Air Force Museum.

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