The Bristol Blenheim IV, entering Coastal Command service in late 1939, became its most widely used variant by 1940. Employed in roles such as coastal patrol, reconnaissance, and shipping protection, it suffered high losses due to vulnerability to enemy fighters. Some Blenheims were modified into long-range fighters as the Blenheim IVF, equipped with a four-gun under-fuselage pack and a mid-upper turret for added defense. Operating with a three-man crew, 254 Squadron flew these aircraft from Aldergrove, Northern Ireland, between May 1941 and June 1942.