When the US entered World War II, its best fighter was the Curtiss-Wright P-40 Warhawk. Although not a bad design in itself, it was nevertheless outclassed by most contemporary European aircraft and was no match for the Japanese Zero in the Pacific but despite this a large number of aircraft were built and served in all fronts. First to use them were the French during the German invasion and managed to destroy 311 Luftwaffe aircraft despite being outnumbered and outperformed. The British were another early operator of the type, naming them Tomahawks and Kittyhawks and they performed quite well especially in North Africa with the Desert Air Force whereas US P-40s were mostly used in the Pacific and were relegated to ground-attack roles once better fighters came into service. Perhaps their most famous contribution to the war was with Gen. Chennault's Flying Tigers which operated from Chinese bases months before Pearl Harbor, they were the first US pilots to face the Zero and gave a good account of themselves, destroying nearly 300 enemy aircraft to only a dozen losses despite flying an inferior machine. The P-40 was eventually used by over 20 countries worldwide including various Commonwealth nations and the Soviet Union.

The Warhawk first flew as the XP-40 in 14 October 1938, initially it was merely a conversion of the P-36A with an Allison inline engine. The first production units were known simply as the P-40 but soon large orders of P-40As were made by the USAAF as well as the RAF. The "Flying Tigers" flew P-40B and P-40Cs, the latter which had self-sealing fuel tanks and provision for a drop tank. The next major development was the P-40D, it featured a shortened nose and was renamed Kittyhawk by the RAF which used it extensively while the USAAF preferred the P-40E with upped the defensive armament to 6 guns. Meanwhile, the P-40F substituted the Allison engines with the Packard-built Rolls-Royce Merlin for increased altitude and climb performance. The second Merlin-equipped variant was the P-40L though in the event many ended up being re-engined with the older Allisons due to a shortage of Merlin spares. The last and definitive Warhawk variants began with the Allison-engined P-40Kand M which were recognizable by the lengthened fuselage which had been introduced in the earlier Merlin versions. The most widely produced variant was the P-40N with a lighter structure and a significant bomb load capability, some featured frameless canopies as well as other lesser technical differences. As was mentioned earlier, RAF aircraft were named differently than their USAAF equivalents, early versions were designated Tomahawk Mk. I (P-40), Mk. IIA (P-40B), and Mk. IIB (P-40C) while later models were referred to as the Kittyhawk Mk. I (P-40D), Mk. IA (P-40E), Mk. II (P-40F) and the Mk. IV (P-40N).