Supermarine Sea Urchin
 The Supermarine Sea Urchin was an unbuilt British racing biplane flying boat designed by the Supermarine Aviation Works to compete in the 1924 Schneider Trophy. It was to be a single seat biplane powered by a Rolls-Royce Condor V-12 water-cooled engine buried in the fuselage driving a pusher propeller mounted on the upper wing via geared shafts. It was abandoned without being built owing to problems with the engine and the transmission required to drive the propeller.