Choosing engines for the P.139B naval aircraft

What Rolls-Royce engine might the P.139B have used if the aircraft had been made to work?

Probably a customized derivative of an available turbojet, with the choice driven by whether cruise efficiency or top speed took priority.

No single production engine is presented as inevitable for the P.139B. A customized installation derived from one of the turbojets available to the British aircraft industry is considered more likely. The exact choice would depend on whether designers optimized the aircraft for economical cruise or maximum speed. Propulsion was therefore part of the wider mission tradeoff rather than a component that could be selected independently of the planned flight profile.