Specs for high-altitude interceptor, which led to Lightning, issued 1937. Many designers thought specs could not be met, but H. L. Hubbard and "Kelly" Johnson of Lockheed proposed twin-engine design with twin booms. To impress USAAC, Feb 39, only prototype flown coast-to-coast in record time of 7 hrs 2 min (but crashed on final). First 30 conformed to prototype design, but optimum configuration not achieved until D model. Nov 41, E appeared with more powerful armament. Beginning of 42, F appeared and was first to be used on a large scale in Europe (toward mid 42) and in North Africa in Nov. Lack of cockpit heat made it very uncomfortable at high altitudes over Europe but no problem over Africa and the Pacific. G (1082) and H (601) models followed. Then came J (2970), one of the most widely used; more powerful engines, greater armament, and boosted ailerons made it much easier to handle and very effective. L model (3923) had larger engine (1475 hp) but otherwise similar to J. Some J and L models used as bombers with adoption of glazed nose for bombardier. Last model was M designed as a night fighter; configuration changes permitted addition of second crewman--behind and slightly above pilot's cockpit--as well as radar, navigation, or precision bombing equipment. With bomb load greater than B-17s and -24s, P-38s very effective in ground attack role. About one in eight of all P-38s used for photo reconnaissance.