It ushered in Electronic countermeasures (ECM) warfare, jamming enemy radar installations from October 1942 as the only such squadron in the RAF initially.

The squadron was formed from Defiant Flight, also known as Special Duties Flight – an electronic countermeasuress unit equipped with the Boulton Paul Defiant Mk.II – at RAF Northolt on 1 October 1942,[5] It moved to RAF Heston later that month.

As part of 11 Group, 515 Sqn performed radar jamming duties, using Moonshine and Mandrel equipment.

At the time of its disbandment on 10 June 1945, 515 squadron had carried out 1,366 operational sorties with the Mosquito with a loss of 21 aircraft, with most of its aircrew transferring to No.

Mandrel, developed at the TRE and also built in the United States as AN/APT-3, was the code-name for a jammer deployed against Freya and Würzburg radars used by aircraft of 515 sqn and 100 Group.