In early 1941, Saab and the aircraft designer Frid Wänström accompanied by his team, started the study of a new fighter for the Swedish Airforce.This new fighter utilized the powerful German engine DB 605B as a pusher mounted between twin booms.The pushing propeller however, created a need for the designers to develop an ejection seat, which made the J21 one of the first fighter aircraft in production to be fitted with an ejection seat.

The J21 was Sweden's first fighter aircraft with ”tricycle landing gear”.The heavy armament of one 20mm cannon was mounted in the nose together with two 13mm machine guns, and two 13mm machine guns were mounted in the wings.This provided provided several key advantages.

The first J21A took flight in July 1943 with SAAB chief test pilot Claes Smith at the controls which was followed by operational service into late 1945.

A total of 297 J21 aircrafts fitted with theV-12 engine were delivered from 1945 in 3 versions,21A-1,A-2 and A-3.This kit depicts the J21A-3 version which utilized updated machine guns and a cannon made from Bofors. The updated J-21 also carried rockets and bombs and included other updates.

The performance on the V-12 powered J21 was generally good with very tight turning circle on low altitudes while featuring heavy and concentrated firepower from the massive guns. Limitations were with poor rearward visibility and heavy controls, making air combat tiring.

The SAAB J 21A was phased out from service after 1954 with most of the airforce aircrafts being replaced with the jet-powered deHavilland J28 Vampire and SAAB J29 Flying barrel.