 Additionally, the company decided to construct a third prototype, powered by the more powerful Alvis Leonides Mk 25 radial engine.On 24 February 1950, the Armstrong Siddeley Cheetah-powered prototype serial number "WE522" performed its maiden flight.Months later, an extensive evaluation was performed of the Provost prototypes, which was flown head-to-head with the rival H.P.R.