Defending our skies

Last Updated: 27 Jun 2017
How Signals Intelligence helped combat air raids in World War I.

By James Bruce, Researcher, GCHQ Authorised History

Whilst the Battle of Britain is firmly lodged in the British psyche, German air raids and the British response during World War I are relatively unknown. This is not surprising - although night-time raids by Zeppelins and aeroplanes, and for a period in 1917 daylight aeroplane raids, caused public fear and outrage, they were strategically insignificant and no threat to national survival. But, like the Battle of Britain, this was an air defence campaign fought at the leading edge of technology and Britain's response, including the use of Signals Intelligence, laid the foundations for World War II.

The army was given control of the air defence of Great Britain in June 1916 - until then responsibility had been untidily split between the Admiralty and the War Office with their respective Signals Intelligence organisations, Room 40 and M.I.1(b), both working against aircraft communications. As part of the new arrangements the areas of M.I.1 (b) responsible for wireless interception, direction finding (D/F) and traffic analysis were split off into a new section called M.I.1 (e), with support to air defence as its main operational task.

M.I.1 (e) was headed by Major Adrian Simpson, who at the outbreak of war was the managing director of the Marconi wireless company's Russian subsidiary. After a period spent trying (largely unsuccessfully) to improve Russian communications and communications security he returned to Britain in 1915 and joined M.I.1 (b). Simpson was an enterprising character, as one of his officers recalled: "If he wanted something and the War Office refused it, he tried the Admiralty, who generally granted it to score off the War Office. If the Senior Service failed there was still the Air Force, or even the Post Office, which last he actually persuaded to put up three direction-finding stations at their own expense and to provide all the men to run them."

M.I.1 (e)'s main intercept site was at Devizes, taking advantage of aerials erected before the war as part of the Imperial Wireless system, with D/F carried out by small purpose built sites at Peterborough, Westgate-on-Sea, Leiston, Seaham Harbour, Falkirk and on the War Office roof, the last using an "8 foot square wooden frame aerial on a scaffolding pole - rotated mainly by a motor car wheel and brute force".

Working in cooperation with British and French Signals Intelligence units in France and with Room 40, M.I.1(e) was able to give advance warning of air attacks and then track the raiders' approach using D/F. They were helped by the difficulties of night-time navigation - to fix their positions German aircraft often made transmissions intended to allow their own D/F system to locate them and inform them of their whereabouts, an obvious windfall for British Sigint.

M.I.1(e)'s reporting, together with information from ground observers and sound location, was fed into a plotting and command system - the London Air Defence Area (LADA) - whose structure and efficiency in 1918 matched that of Fighter Command in 1940; but however good the system for collecting and plotting information, the defenders' ability to respond was limited by technology. The lack of accurate real time positional information (D/F did not provide pinpoint accuracy) and, until very late in the war, the absence of radio communications with aircraft meant fighters could not be vectored to an intercept 1940-style, but could only be launched to operate on the general track of raids. By 1918 the British were destroying about 10% of the aircraft launched against them, but far more were lost through navigational errors and crashes on landing.

The inevitable post-war rundown saw the dismantling of most Signals Intelligence facilities in Britain, but in 1927 the RAF established an intercept site at Waddington under Warrant Officer WG Swanborough (Swannie), who had begun his Signals Intelligence career as a wireless operator at the Leiston D/F site in 1918.


9 men in WWI uniform posing in front of a large shed and field
The Leiston Directon-Finding site in 1918. 'Swannie' is front row, right. ©Crown Copyright


For Fighter Command in 1940 this site, by then located at Cheadle, and its associated network of D/F sites fulfilled the same function as M.I.1(e) had for LADA in 1916-18. In the Battle of Britain advances in technology - fine grain tracking from radar and the ability to direct fighters using radio – meant the defenders were better able to counter raids, but the underlying information processing and command structures were those developed to counter 'Zepps', 'Gothas' and 'Giants' over two decades previously. And they worked.


An illustration of a 'zeppelin' being shot down in flames, lit by searchlights.
British Propaganda Postcard 1916. ©Public Domain