The J2F Duck was an improved version of the JF, with its main difference being a longer float.

[2] The more obvious external appearance clue to distinguish a JF from an early J2F is the deletion of the inter-aileron strut between the wings on the J2F; less noticeable perhaps is the J2F's slightly longer rear fuselage/float joining fillet beneath the tail.

[2] The Duck's main pontoon was part of the fuselage, almost making it a flying boat, although it appears more like a standard aircraft with an added float.

These early production series had provisions for mounting a machine gun at the rear seat facing aft, as well as a single bomb rack mounted under each wing, capable of carrying a 100 lb (45.4 kg) bomb or depth charge on each.

Ducks served as general/utility amphibians for photographic, target-towing, scouting, and rescue work.