I can not give any details of the Valiant days as I was not there. However on the Victor Mk 1 Tanker we had a crew on short notice standby (I seem to remember 1 hour) to launch as ACP. This was not an Airborne Command Post as there was only the standard crew aboard, no senior officer commanders. The role of the aircraft was as an Airborne Communications Post to rebroadcast go on/come back codewords to the bomber force en route to their targets.