The decline of the Spitfire was due to its having been conceived as a light, fast racehorse of a fighter, and then saddled with bigger and bigger engines and propellers that eventually overwhelmed its airframe. Increased power was inevitable; it meant higher speed, better acceleration and climb, and the ability to carry more formidable armament, but there also had to be a proper proportion between power and size. The dates of inception of various fighter designs correlate with the availability of increasingly powerful engines. The Mustang, faster than the Spitfire but inferior in climb and maneuverability, was similar to it in size and, like it, conceived for an engine of about 1,000 hp. Then, with the arrival of 2,000 hp engines, such as the Rolls-Royce Griffon and the Pratt & Whitney R-2800, came increasingly massive fighters like the Typhoon, Tempest and Corsair, and the gigantic Thunderbolt. Pilots, conversely, as may be seen in photographs from the period, became proportionately smaller.