pr00ne... Fast jets... No: but what about helicopters and transports?
It's tradition (you may need to look that concept up... stands by for incoming)... the RN have painted ROYAL NAVY on aircraft since they took control of the Fleet Air Arm back from the RAF in the 1930's
What the RAF could do though (whilst we're on the subject of markings) is stop claiming the UK National marking as being an "RAF Roundal"... the AAC, RM and RN all carry it with pride
(Thinks: maybe that's why the newspapers/TV keep on getting it wrong in their articles.... hmmmm?)