Thank you, Guys!
At the end of the Thirties the USN was experimenting together with their suppliers in which way their fighters would be develop. Some engineers stayed with their biplane concept and others were changing from biplane to monoplane. The only monoplane fighter at that time was the F2A Buffalo, but the Navy was not fond of the plane and their competitor , the XF4F-2 monoplane, was although faster but less maneuverable. So Grumman fell back to their F3F and made an monoplane version - the F3F-2M -, at the same time they changed the fuselage of the XF4F-1 with its biplane wing and came with a faster and maneuverable F4F-1.
Both planes were delivered to the USN. Here are the two examples:
regards
Lauhof