The P-40M was similar to the K series. Originally it was intended solely for the RAF. An Allison V-1710-81 Engine replaced the Merlin. A perforated cooling grill was added just forward of the exhaust stubs and a set of reinforced ailerons were installed. The M was a long fuselage aircraft distinguishable from the K by virtue of the radio mast. Three .50 machine guns were carried in each wing.