The Fr-37 design started development in late 1937 and was put into service by 1939

Armament:
2x .50 mg fixed firing forward from the wings
(250 rpg)
1x 20mm cannon in the turret
(30rds per mag with room for 4 mags although 3 mags were standard)

Engine:
Allison V-1710 (1,200 hp)

Top speed:
321 mph

Crew: 2
Pilot
Gunner/radio operator

The aircraft was liked by pilots as it had great landing characteristics and good flying performance. In 1940 the yugoslav airforce requested a bomber escort model with 4 .50 mgs in the turret, a new engine to increase the top speed by 20 mph, and add drop tank capabilities.

Production ended in 1943 with ~400 being produced.

In late 1943, ~40 aircraft were converted to target tugs.

Ag2 is for turret

Ag4 is for gyroscope