First flown in August 1937, the Boulton Paul Defiant did not participate in operations until 12 May 1940 during the Battle of Britain. An unusual design, the initial surprise afforded by a rear-firing four gun powered turret accounted for 65 enemy aircraft. However, once the aircraft's weaknesses were identified, by August 1940, losses of Defiants were so great that they were withdrawn from front-line duties and transferred to night fighting duties.

In this latter role, two RCAF squadrons were equipped with Defiants. Nos 409 and 410 Sqns both used the aircraft type briefly but without any success.