In October 1937 the Naval Aeronautical Establishment formed a plan for the 12-Shi Experimental Fighter (later called Zero-Sen), a new fighter to succeed the 96 Kansen which was expected to have a maximum speed of more than 500 km/h and apeed well over that of the 96 Kansen. Heavy armament consisting of two 20mm machine guns; maneuverability not inferior to that of the 96 Kansens; and a longcrusing range corresponding to over 6-8 hours; flight at a cruising speed which was based on combat experience in China. The Naval Aeronautical Establishment made a request to Nakajima Aircraft and Mitsubishi Aircraft for competitive trial manufacture. Mitsubishi's deign staff led by engineer Jiro-Horikoshi, who had previously designed the masterpiece plane 96 Kansesn, set to work. Increased cruising range and speed naturally required large horsepower, engine and fuel capacity and therefore large fuselage. In the basic design, the 12-Shi Kansen was two times as heavy as the 96 Kansen. Pilots who attached the greatest importance to maneuverability made complaints and requested that the new fighter should be made smaller. On the other hand, some people took a stand against them saying that maneuverability could be made up for by training and skill and that greater importance should be attached to speed and cruising range which could not be compensated for by training or skill. No definite conclusion could be reached on this matter and Mitsubishi designers continued to be troubled with the severe figures prescribed. Horikoshi and his designers firmly believed that they could save weight by using Extra Super-Duralumin which Sumitomo then developed through increasing conventional duralumin in strenght and by taking other drastic measures for lightening the fuselage. They proposed the view to the Naval Aeronautical Establishment and gained the approval.