 As flown, the Type 138 was a single-engine, low-wing monoplane with a fixed, tailwheel undercarriage.From the outset it was designed as a dedicated research aircraft capable of reaching high altitudes; aeronautical engineer Frank Barnwell had first proposed the design to the British Air Ministry during November 1933.The revised design was produced in response to the issuing of Specification 2/34 by the Air Ministry during June 1934.