If I remember correctly from my long past association with the Andrew, destroyers and submarines are boats, not ships. Is that still the case?
Ooh, first post.
<PEDANT>
Submarines are called boats, Destroyers are not, they are ships. Destroyers are ships as they are
designed for
sustained deep water operations. Submarines are still called boats by dint of their historical development from semi-submersible motor-torpedo boats, and that the first ones would be carried on ships to their target area.
A general rule of them is often applied, "ships can carry boats, but boats cannot carry ships" (hence it could be argued that a submarine is not a ship as it cannot carry boats, bar special forces.. Oh never mind). This is rather to simplistic as many mega yachts can carry boats, but shouldn't be classified as ships as they are not deigned to operate effectively in the middle of, for example, the North Atlantic. They may be capable of such a voyage in benign conditions, but are not deigned so to do.
(/PEDANT>