Wow what a grid. I particularly liked the concise explanations of the groups. And the straightforward not at all obscure nature of the groupings. grid setters could learn a lot from this grid

What sort of pimply little nerd (who has no sex might I add) knows what prefixes are used for navy ships on other countries. I bet your Dad drinks to numb the pain of how absolutely pathetic and lowly you are. And your mother, well chances are she's run off with a sailor or something daft like that you feckless little whelp. I reckon you ought to knuckle down and, if you can quite manage it, you human sphincter, make a better grid next time as this is the absolute nadir of PuzzGrid you infantile pant-pooing bumhead.
-davo