True. The Spitfire and many other top-line 1940 planes also lacked armor for the pilot (at first, anyway). That included the first P-40s. The Wildcats in service in 1941 apparently already had armor, though. Plus, the more powerful American engines (made possible by higher-octane gasoline than the Japanese had) was also a major factor; the stronger engines could lug around the heavier airframes with greater ease, and the top speeds of the Zero and Wildcat were just about the same. The Zero had better climb performance, but the Wildcat could dive faster.