and trailing edges was economic, the latter design could be manufactured with greater efficiency. Perhaps the aircraft company most commonly associated with the elliptical wing was the British manufacturer Supermarine. During the early 1920s, the company's chief designer, Reginald Mitchell, had developed the Supermarine S.4, a British elliptical wing racing seaplane; it conducted its first flight during 1924. While the S.4's direct successors featured a wing designed by a different designer, Mitchell remained a proponent of the planform. By 1934, Mitchell and his design staff were engaged in designing a new fighter aircraft for the Royal Air Force. They decided to use a semi-elliptical wing shape to solve two conflicting requirements; the wing needed to be thin to allow a high critical Mach number but it had to be thick enough to house the retractable undercarriage, armament, and ammunition. An elliptical planform is the most efficient aerodynamic shape for an untwisted wing, leading to the lowest amount of induced drag. The semi-elliptical planform was skewed so that the centre of pressure, which occurs near the quarter-chord position at all but the highest speeds, was close to the main spar, preventing the wings from twisting. The Spitfire conducted its maiden flight on 5 March 1936. Mitchell has sometimes been accused of copying the wing shape of Heinkel's He 70. Communications between Ernest Heinkel and Mitchell during the 1930s establishes Mitchell's awareness of the He 70 and its performance. However, Beverley Shenstone, the aerodynamicist on Mitchell's team, observed that: "Our wing was much thinner and had quite a different section to that of the Heinkel. In any case, it would have been simply asking for trouble to have copied a wing shape from an aircraft designed for an entirely different purpose." Almost all Republic P-47 Thunderbolts, an American fighter aircraft, were outfitted with elliptical wings; only the last production models different, instead featuring squared-off wingtips, akin to the low-altitude Spitfire variants. The Aichi D3A, a Japanese dive bomber operated by the Imperial Japanese Navy, also used an elliptical wing that bore considerable similarity to that of the He 70. The Mitsubishi A5M fighter also utilized an elliptical wing design. Several other types had planforms which differed relatively little from the elliptical. The Hawker Tempest II fighter aircraft, which later developed into the Hawker Fury and Hawker Sea Fury, also utilised a near-eliptical wing planform, although squared off at the tips. Since 2009,