London District Signals was a headquarters signal unit of the Royal Engineers (RE) and later Royal Corps of Signals in Britain's Territorial Army from 1908. It served with a corps headquarters at Gallipoli and on the Western Front during World War I, and later became an air defence signal unit during World War II. Its successor unit continues in the Army Reserve today.

The London Electrical Engineers was a Volunteer unit of the British Army's Royal Engineers founded in 1897. It pioneered the use of searchlights (S/Ls) for port defence before World War I and for anti-aircraft (AA) defence during the war. In the interwar period it formed the two senior searchlight regiments of the Territorial Army, which defended Southern England during The Blitz. Detachments later served in the Battle of Crete and Siege of Tobruk.