Though never used by the USAAF, the Martin Baltimore was derived from the Martin 167 bomber (Maryland) at the request of the British Purchasing Mission to modify the aircraft since the Maryland lacked communication between the two front crew members and the rear gunner. This new aircraft, the Martin 187, was christened the Baltimore and entered RAF service in 1942 retaining the wings and tail surfaces of its predecessor but with a new deepened fuselage and more powerful engines. It was employed primarily as a light bomber but also for anti-shipping and photo-reconnaissance duties in the North African and Mediterranean campaigns with the RAF, the South African Air Force and the Italian Co-Belligerent Forces which used the Baltimore over Yugoslavia and the Balkans (other users were Australia, Greece, and Turkey). They remained in RAF service until early 1946, one squadron operating it from Kenya.

The Martin 187 prototype flew for the first time on 14 June 1941 and entered RAF service as the Baltimore Mk. I in 1942. Subsequent variants were the Mk. II with a twin dorsal guns, and the Mk. III or Mk. IIIA with a Boulton Paul dorsal turret and improved engines. Later, the Mk. IV had a Martin dorsal turret installed and finally, the Mk. V featured an upgraded R-2600-29 engine. This last version was also the most widely produced with 600 examples built.