The Airacobra saw combat throughout the world, particularly in the Southwest Pacific, Mediterranean and Russian theaters. Because its engine was not equipped with a supercharger, the P-39 performed best below 17,000 feet altitude, and it often was used at lower altitudes for such missions as ground strafing. When P-39 production ended in August 1944, Bell had built 9,584 Airacobras, of which 4,773 had been allotted to the Soviet Union. Russian pilots particularly liked the cannon-armed P-39 for its ground attack capability. Other P-39s served French and British forces.