Old RN - there was never a real plan to invade Rhodesia - the Tories were dead set against it and most of the country didn't support the idea. Harold Wilson was far too downy a bird to get involved in a pointless war far far away that wasn't going to benifit the UK - remember his views on helping the Yanks in Vietnam.
Plus, IIRC, papers such as the Torygraph and the Excess were running stories "that British servicement would refuse to fight" Smith's mob.
The Admirals, as ever, were trying to hang on to as many assets as possible especially in warm waters - Wilson used the whole RAF/RN operation as a low cost, low risk cover so he could face the UN and the Commonwealth and show he was "doing something"