Try "To Rule the Waves, how the British Navy shaped the modern world" by Arthur Herman. He's a septic so it's not jingoistic but gives a good overview from 1652 to 1982. Again it's a long read but worth it IMO.
Edited to add Johansen got in before me but 2 recommends can't be bad
I'd recommend Admirals by Andrew Lambert a good general one with bios on most major British admirals from the Armada to WWII and background info on the transformation of the navy in that period. Be handy for the naval history questions and give you some ammo if, like the army selection board, they ask you to give examples of figures who you respect/are inspired by.
Look on amazon or play.com, for a book called: Why should britain tremble.
Its about a guy ( changed name on book, known as chas cooke ) writing a book about his navy life, from when he joined his first ship to leaving. Good read, and i dont really like reading but managed that book as it kept me wanting to read on.
Thanks for all the replies, I actually went for Admirals by Lambert as Swansea Waterstones have an appalling selection of Rn related literature..
Really enjoying it and keeping an eye out for the others too...
Libraries have quite a vast collection of books such as these, a lot are probably held in central stores but most authorities charge under £1 to have them sent to a local library. Portsmouth Central library holds every single book re: Royal Navy history for example (can be sent via inter library loans). Not only is it cheaper but can still make notes on post its and stick them in; plus of that rather than writing in a book is you can keep them and make a revision wall or something! People underuse libraries, getting a card is freeeeee and everything. Then if you find one you really like invest in it if you are a slow reader can renew them- libraries 4ever.