There is only one ship in the British Royal Navy.

If I was being completely pedantic (and I am), more pedantic that even Webster 1913, a ship is a three-masted, square-rigged sailing vessel. (See entry number 2, "Specifically"... in Webbie's entry below.) Hence, the only ship in the Royal Navy is HMS Victory, preserved at Portsmouth since some time shortly after the Battle of Trafalgar.

Other vessels in the Navy are (technically) known as frigates, destroyers, corvettes, minesweepers and so on.

Even die-hard anchor-faced sailors don't insist on the use of the word ship in such a narrow manner, unless they're being pedantic (as I've already stressed I'm being right now). The pronunciation of 'Lieutenant' is a different matter.