Of warships (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
naval
'of warships' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for naval that I've seen before include "Relating to marine force" , "Of seaborne forces" , "Relating to nautical defence force" , "Maritime" , "To do with the marine branch of an army" .)