High Quality Content by WIKIPEDIA articles! A naval trawler is a vessel built along the lines of a fishing trawler but fitted out for naval purposes. Naval trawlers were widely used during the First and Second world wars. Fishing trawlers were particularly suited for many naval requirements because they were robust boats designed to work heavy trawls in all types of weather and had large clear working decks. One could create a mine sweeper simply by replacing the trawl with a mine sweep. Adding depth charge racks on the deck, ASDIC below, and a 3-inch (76-mm) or 4-inch (102-mm) gun in the bows equipped the trawler for anti-submarine duties.