Every single "operation" is sort of overkill, I think, and won't group very many profiles, which is the point of categories in WikiTree. I believe their units are more important categories to add
The trawlers could be added. Ships are usually added with hull number, but if that's not known (I can't find any here), then the naming would be [[Category:HMT Gaul, Royal Navy, World War II]] (UPDATE:I created the category for you)
You would explain his positions aboard the different boats/ships in the biography. His profile could also have the WWII sticker applied. In the units paramater (units=) you could list the trawlers, and in the unit parameter (unit=) you could list one of the trawlers (example: unit=HMT Gaul). Branch parameter (branch=) would be branch=Royal Navy.