The Pratt & Whitney R-4360 Wasp Major is an American 28-cylinder four-row radial piston aircraft engine designed and built during World War II.

At 4,362.5 cu in (71.5 L), it is the largest-displacement aviation piston engine to be mass-produced in the United States, and at 4,300 hp (3,200 kW) the most powerful.

Its main rival was the twin-row, 18-cylinder, nearly 3,350 cu in (54.9 L) displacement, up to 3,700 hp (2,800 kW) Wright R-3350 Duplex-Cyclone, first run some seven years earlier (May 1937).

[2] The four-row configuration had severe thermal problems that decreased reliability, with an intensive maintenance regime involving frequent replacement of cylinders required.

Owing in large part to the maintenance requirements of the R-4360, all airplanes equipped with it were costly to operate and suffered decreased availability.