P-36A Ser No 38-174 was withdrawn from squadron service early in 1939
and fitted with four belt-fed 0.30-in machine guns in the wings. At
the same time, the fuselage mounted armament was changed to a pair of
0.5-in machine guns. Thus armed, the modified aircraft was
redesignated XP-36D.
Sources:
-
Curtiss Aircraft, 1907-1947, Peter M Bowers, Naval Institute Press,
1979
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The Curtiss Hawk 75, Aircraft in Profile No. 80, Profile
Publications, Ltd. 1966
-
War Planes of the Second World War, Fighters, Volume Four, William
Green, Doubleday, 1961.
-
Air Enthusiast, Volume 1, William Green et al, Doubleday, 1971.