flew for the first time in 1927. A paper by Mitchell on the use of the Southampton appeared in the March 1926 edition of Flight magazine. In 1928, a flight of Supermarine Southampton IIs left Felixstowe on 14 October for Australia, and returned to the UK on 11 December. The expedition provided Mitchell's design team with valuable information about operating aircraft in the tropics. The Southampton was one of the most successful flying boats of the between-war period, and established Britain as a leading developer of maritime aircraft. It was used to equip six RAF squadrons up to 1936. In 1926, the Air Ministry issued specification 21/26 as a way to address the need for new fighter aircraft, and Mitchell's design team, which he had re-organised that year into separate drawing and technical offices, responded with a number of designs, including the Single Seat Fighter. By this time, Supermarine was moving away from wooden amphibious aircraft. The company concentrated instead on designing larger metal flying boats, such as the 3-Engined Biplane Flying Boat, designed in November 1927. The Supermarine Air Yacht, and a new design, the Southampton X (not related to other planes with the same name), was ordered in June 1928. Mitchell dispensed with the complicated curved surfaces for the wings and the hulls of the Air Yacht and the Southampton X, and as a result these aircraft appeared "boxy". Specification R.6/28, issued in 1928, resulted in a series of designs by Supermarine for a six-engined flying boat, with one of designs being a radical departure for Mitchell—it had a newly-designed cantilever wing with a large surface area and cross section. The aircraft was never built. From 1929 to 1931, he continued to design aircraft based on the Southampton and the Southampton X, such as the Supermarine Sea Hawk and its variant the Sea Hawk II, the Type 179, the Nanok and the Seamew. New designs, production orders and patents (19291934) In February 1929, Mitchell submitted patent GB 329411 A, "Improvements in the Cooling System of Engines for Automotive Vehicles", a condenser to be placed within the wings of an aircraft. The Air Ministry rejected Supermarine's proposal for such a wing-cooled aircraft, but in May 1929 a new specification allowed Mitchell to use his ideas again. A similar patent was submitted in 1931. The condenser was used in the Type 232, produced in April 1934, which was never put