In the late 1930s, the USAAC was planning to expand its force, and on January 25, 1939. manufacturers were invited to submit proposals for pursuit aircraft. The Army was still thinking in terms of low-altitude, short-range fighters. Among the contenders were the Lockheed XP-38, the Bell XP-39, the Seversky/Republic XP-41 (AP-2) and XP-43 (AP-4), and no less than three planes from Curtiss, the H75R, XP-37, and XP-42. Although the XP-40 could not match the performance (especially at altitude) of the turbosupercharged types, it was less expensive and could reach quantity production fully a year ahead of the other machines. In addition, the XP-40 was based on a already-proven airframe that had been in production for some years. Consequently, on April 26, 1939, the Army adopted a conservative approach and ordered 524 production versions under the designation P-40 (Curtiss Model 81). At that time, it was the largest-ever production order for a US fighter, and dwarfed the service test orders placed that same day for YP-38 and YP-39 fighters. A couple of weeks later, 13 YP-43s were also ordered.
The P-40 was similar to the final XP-40 configuration except for the use of 1040 hp V-1710-33 (C15) engines. The armament was the standard USAAC armament of the day-two 0.50-inch machine guns, mounted in the upper nose and synchronized to fire through the propeller arc. Provisions were made for the mounting of one 0.30-inch machine gun in each wing. Flush riveting was used to reduce drag. Armor, bulletproof windshields, and leakproof fuel tanks were not initially fitted, were later added to the aircraft while it was in in service. The P-40 was a relatively clean design, and was unusual for the time in having a fully retractable tailwheel.
The first flight of a P-40 (Ser No 39-156) was on April 4, 1940. Maximum speed was 357 mph at 15,000 feet, service ceiling was 32,750 feet, and initial climb rate was 3080 feet per minute. An altitude of 15,000 feet could be reached in 5.2 minutes. Cruising speed was 272 mph, landing speed was 80 mph, and the range at 250 mph was 950 miles. The length of the P-40 was 31 feet 8 3/4 inches, which became standard for all early models. Weights were 5376 pounds empty, 6787 pounds gross, and 7215 pounds maximum.
Deliveries of the P-40 to Army units began in June of 1940. Three of the P-40s were used for service testing, the USAAC contract making no provisions for the standard practice of supplying YP models. They were delivered with full camouflage applied-olive drab on the top and grey on the undersides. The standard rudder stripes and star insignia were applied to both wings.
The first USAAC units to operate the P-40 were the 33rd, 35th and 36th Pursuit Squadrons of the 8th Pursuit Group, based at Langley Field, Virginia (later transferred to Mitchell Field, New York). It was soon followed by the 55th, 77th, and 79th Pursuit squadrons of the 20th Pursuit Group based at Hamilton Field, California, the 31st Pursuit Group (39th, 40th, and 41st squadrons) based at Selfridge Field, Michigan. and the 21th, 34th, and 70th Pursuit Squadrons of the 35th Pursuit group which trained on P-40s prior to being issued with P-39s. Later came the 37th Pursuit Group (28th, 30th, 31st squadrons) based in the Panamal Canal Zone, the 16th Pursuit Group (24th, 29th, 43rd squadrons) also based in the Panama Canal Zone, the36th Pursuit Group (22nd, 23rd, 32nd squadrons) based in Puerto Rico, plus the 15th and 18th Pursuit Group based at Wheeler Field in Hawaii.
Foreign air forces were beginning to take notice of the P-40, and in May of 1940, the Armee de l'Air of France placed an order for 140 H-81As (export model of the P-40).
Only 200 of the initial P-40 order were actually completed as P-40s. Serials were 39-156/280 and 40-292/357 (c/ns 13033/13232). In September of 1940, the remaining 324 aircraft of the initial order had their delivery deferred to enable Curtiss to expedite the delivery of the 140 French-ordered H-81As. The first export aircraft had actually been completed in French markings in April of 1940. However, none of these machines actually reached France before the June 1940 Armistice, and the contract was taken over by the Royal Air Force as Tomahawk I.
16 P-40s were sent to the Soviet Union after the German invasion.
The P-40 lacked such things as armor for the pilot, self-sealing fuel tanks, and a bulletproof windshield, so it was not considered as being suitable for combat. On October 22, 1942, those P-40s still in USAAF service were ordered restricted from combat duty and were redesignated RP-40.