Breakright's correct. When you attend Cranwell, the RAF will put you through part one of their selection proceedure, which consists of the aptitude tests, initial medical, and interview. The Navy simply utilise the RAF's aptitude testing facilities, and any successful candidates will be invited down to Dartmouth to attend the Admiralty Interview Board - the Navy equivalent of the RAF's selection proceedure. Couldn't comment on the standards required for the two services, although I think I'm right in saying that the Navy have lower aptitude demands than the RAF.
Good luck anyway!