 The specification, which called for a pair of prototypes, sought an aircraft that would be capable of achieving the unheard-of altitude of 50,000 feet; it had been issued in response to public pressure in favour of government sponsoring of such record attempts.In addition to Bristol's own work on the Type 138, the Royal Aircraft Establishment (RAE) and National Physical Laboratory also made valuable contributions to the development effort on designing the type.On 11 May 1936, the Type 138A performed its maiden flight, piloted by Cyril Uwins.