US prototype from the late 1930s for a carrier based fighter with twin engines for increased survivability. Grumman struggled hard to get this right and ultimately succeeded with the much larger Tigercat which was too late to see service in WW2. This model is of an early prototype, later versions were somewhat more conventional in appearance.
The Skyrocket achieved fame of a different kind by becoming the star of the wartime "Blackhawks" comic series.
The spherical recess underneath is for mounting the model on a 6mm BB.x1 x2 (on sprue)