The USAAF issued a requirement for an attack aircraft in 1940, before it had information on World War II combat operations in Europe. Consequently, three prototypes were ordered in differing configurations: the Douglas XA-26 attack bomber with a bomb-aimer's position; the XA-26A heavily-armed night-fighter; and the XA-26B attack aircraft with a 75mm cannon. After flight testing and careful examination of reports from Europe and the Pacific, the A-26B Invader was ordered into production, and initial deliveries of the 1,355 built were made in April 1944.

The A-26B had six 12.7mm machine-guns in the nose, remotely controlled dorsal and ventral turrets each with two 12.7mm guns, and up to 10 more 12.7mm guns in underwing and underfuselage packs. Heavily armoured, and able to carry up to 1814kg of bombs, the A-26B was potentially a formidable weapon. Moreover, its two, 1491kW Pratt & Whitney R-2800 engines conferred a maximum speed of 571km/h, making the A-26 the fastest US bomber of World War II. Invaders'remained in USAF service until well into the 1970s.

Missions with the 9th Air Force in Europe began in November 1944, and at the same time the type became operational in the Pacific. The A-26C with a bomb-aimer's position and only two guns in the nose entered service in 1945, but saw only limited use before World War II ended. A-26C production totalled 1,091. With little employment ahead of them, so far as anyone could see, one A-26B and one A-26C were converted to XJD-1 configuration, this pair being followed by 150 A-26Cs converted as target tugs for the US Navy with the designation JD-1; some were converted later to launch and control missile test vehicles and drones, under the designation JD-1D. These designations became UB-26J and DB-26J in 1962.

USAF A-26B and A-26C aircraft became B-26B and B-26C in 1948, and retained this designation until 1962. Both versions saw extensive service in the Korean War, and were again used in a counter-insurgency role in Vietnam. A special COIN version with very heavy armament and extra power was developed by On Mark Engineering in 1963, a prototype being designated YB-26K and named Counter Invader. Subsequently about 70 B-26s were converted to B-26K standard, 40 later being redesignated A-26A. Some were deployed in Vietnam, and others were supplied to friendly nations under the Military Assistance Program. B-26s were used also for training (TB-26B and TB-26C), transport (CB-26B freighter and VB-26B staff transport), RPV control (DB-26C), night reconnaissance. (FA-26C, from 1948 redesignated RB-26C) and missile guidance research (EB-26C). After the war, many A-26s were converted to executive, survey, photographic and even fire-fighting aircraft. Brief details of the two semi-production marks are given in the variants list.