The Short Mayo Composite was a piggy-back long-range seaplane/flying boat combination produced by Short Brothers to provide a reliable long-range air transport service to North America and, potentially, to other distant places in the British Empire and the Commonwealth. Development Short Brothers had built the Empire flying boats which were capable of operating long range routes across the British Empire but could only attempt the trans-Atlantic route by replacing passenger and mail-carrying space with extra fuel. It was known that aircraft could maintain flight with a greater payload than that possible during takeoff. Major Robert H. Mayo, the Technical General Manager at Imperial Airways, proposed mounting a small, long-range seaplane on top of a larger carrier aircraft, using the combined power of both to bring the smaller aircraft to operational height, at which time the two aircraft would separate, the carrier aircraft returning to base while the other flew on to its destination. The British Air Ministry issued Specification "13/33" to cover this project. Design The Short-Mayo composite project, co-designed by Mayo and Shorts chief designer Arthur Gouge, comprised the Short S.21 Maia, (G-ADHK) which was a variant of the Short "C-Class" Empire flying-boat fitted with a trestle or pylon on the top of the fuselage to support the Short S.20 Mercury(G-ADHJ). Although generally similar to the Empire boat, Maia differed considerably in detail: the hull sides were flared and had "tumblehome" rather than being vertical as on the Empire to increase the planing surface (necessary for the higher takeoff weights); larger control surfaces; an increase in total wing area from to ; the engines were mounted further from the wing root to clear Mercury's floats and the rear fuselage was swept up to raise the tailplane relative to the wing. Like the Empire boats, Maia could be equipped to carry 18 passengers. Maia first flew (without Mercury) on 27 July 1937, piloted by Shorts' Chief Test Pilot, John Lankester Parker. The upper component, Mercury, was a twin-float, four-engine seaplane crewed by a single pilot and a navigator, who sat in tandem in an enclosed cockpit. It could carry of mail and of fuel. Flight controls, except for elevator and rudder trim tabs, were locked in neutral until separation. Mercury's first flight, also piloted by Parker, was on 5 September 1937. The mechanism that held the two aircraft together allowed for a small degree of movement. Lights indicated when the