Designed in the late 1930s as a reconnaissance platform, the Saab 18 ended up entering service only until World War II was well underway due to the changing requirements of Swedish authorites which demanded the aircraft also be used for conventional and dive bombing missions. In the event, it would perform all of these roles with different variants equipped additionally with rockets, heavy forward firing cannon and reconnaissance units with cameras and even radar. Like most contemporary Swedish aircraft, the Saab 18 was fitted with locally-copied versions of foreign engines, in this case the Twin Wasp although later models were fitted with the more powerful DB 605 which creatly improved performance. Production of the Saab 18 continued post-war up until 1948 and remained in service until the 1950s most being used for reconnaissance by then.

First flight of the Saab 18A prototype took place on 19 June 1942 after numerous years of development. It entered service as the B 18A bomber and the S 18A photo-reconnaissance platform. The main production version, however, was the B 18B dive bomber with rocket armament followed by the T 18B which began life as a torped bomber but ended up being an attack aircraft with a massive 57-mm Bofors gun.