"We Joined the Navy"
...was part of a series of books by a chap called John Winton, I believe...sort of the RN equivalent of BEagle (!)...
Anyway...the exact details of the RN have undoubtedly changed since then, but the spirit of both the interview process, initial training, and basic sea training remain as described. If you want a bit of light hearted relief then search the 2nd hand bookshops for them. Otherwise, note the wise words posted by others above.
Good Luck!