Brainchild of Ed Heinemann, the Douglas A-26 Invader was designed as a replacement for the A-20 and entered service in 1944. Fast and powerfully armed, the A-26 served with distinction mostly with the 9th Air Force over Europe where its 6,000-lb bomb load and high speed (among Allied tactical bombers, only the Mosquito was faster) made it devastatingly effective but it was later also used in the final stages of the Pacific war. Due to its late entry, comparatively few A-26s were produced (over five thousand were cancelled when the war ended) yet proved so effective as to serve in the Korean War as the B-26 (renamed once the Marauder was retired from service) and also in the Vietnam War where it was one of the preferred aircraft for night strikes against the Ho Chi Minh trail. Among the technologies with the A-26 pioneered were those of double-slotted flaps and remote-controlled turrets while some wartime units were equipped with bombing radar. Post-war, the Invader served in over a dozen air forces although wartime use was limited to the USAAF exclusively.

The first prototype XA-26 flew on 10 July 1942. It was followed by a night fighter prototype, the XA-26A, and then the XA-26B with 75-mm cannon in its nose. Production began with the A-26B which reached Europe in the middle of 1944, this was the most widely produced variant with the other major version being the A-26C which had reduced armament of six .50-in guns and a glazed nose for the bombardier (it was often equipped with bombing radar). Both also flew against Japan in the final stages of the Pacific War. A total of 5,454 aircraft were cancelled after VJ day as well as newer developments one of which included installation of jet engines (the XA-26F). Post-war the Invader was renamed B-26 and served in the Korean as well as the Vietnam War where the B-26K was used as a successful counter-insurgency platform, this aircraft was subsequently renamed A-26A due to the refusal of Thailand to base 'bombers' in their territory.