The Hawker Siddeley P.139B was a proposed airborne early warning aircraft intended to operate from aircraft carriers of the Royal Navy. The P.139B formed part of the a major equipment procurement plan for the RN in the 1960s intended to give the service a force of new, modern carriers capable of operating air groups consisting of equally modern aircraft. However, cuts in defence spending by the British Government in the mid-1960s meant that these proposals never came to fruition.