F-39 95 mm gun

The gun was created as a part of a program to increase the caliber of divisional artillery from 76 mm to 95 mm (improvement in HE performance from going up to 85 mm was considered insufficient, although there was a later 85 mm divisional gun project). However, after the gun passed preliminary trials, the requirements for divisional artillery increased again to the 107 mm caliber and the project died. More detailed photos of the F-28 are available here.