The following is a list of Royal Navy ship names by name in alphabetical order, both past and present. Many of the names have been re-used over the years and thus represent different ships.
(Note that this list still lacks many important ships.)
... Atresia of small intestine[?]
Atrial myxoma, familial[?]
Atrial septal defects[?]
Atrioventricular septal defect[?]
Atrophoderma of Pierini and Pasini[?]
...