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[Creeperopolis]

The Supermarine S.4 was a 1920s British single-engined monoplane built by Supermarine. Designed by a team led by the company's chief designer, R. J. Mitchell, it was built to race in the 1925 Schneider Trophy contest.

Mitchell's design was revolutionary. Aware of the need to reduce drag forces to increase speed, he produced a floatplane that was in marked contrast to the flying boats previously designed by Supermarine. Built of wood, and with an unbraced cantilever wing, it was powered by a Napier Lion engine developed to produce 700 horsepower (520 kW) over a short racing period. The S.4 was aerodynamic and aesthetically pleasing, but the cockpit position was potentially hazardous, as it restricted the pilot's view. Less than a month after its maiden flight on 24 August 1925, it raised the world's seaplane speed record to 226.752 miles per hour (364.922 km/h).

At Bay Shore Park in Baltimore in the US, the venue of the 1925 contest, the S.4's rear end was damaged by a falling pole during a gale prior to the event. During navigation trials on 23 October, the repaired aircraft was observed to be performing well, but then—for reasons that have not been fully explained—it went out of control, and was destroyed when it dived into the sea from 100 feet (30 m), injuring the pilot, Henri Biard.

Mitchell used the practical experience gained from his work on the S.4 when designing its immediate successor, the Supermarine S.5.