The P-40A designation was skipped in the initial designation
assignments. However, it was applied retroactively to P-40 Ser No
40-326 when it was converted to a camera-carrying photographic
reconnaissance model at Bolling Field in March of 1942.
Sources:
-
War Planes of the Second World War, Fighters, Volume Four, William Green,
Doubleday, 1964.
-
The American Fighter, Enzo Anguluci and Peter Bowers, Orion Books, 1987.
-
United States Military Aircraft since 1909, Gordon Swanborough and Peter
M. Bowers, Smithsonian Institution Press, 1989.
-
Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 1979.
-
The Curtiss P-40 Tomahawk, Ray Wagner, Aircraft in Profile, Volume 2,
Doubleday, 1965.