Naval trawler

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 bow equipped the trawler for anti-submarine duties.

Armed trawlers were also used to defend fishing groups from enemy aircraft or submarines. The smallest civilian trawlers were converted to danlayers.

The naval trawler is a concept for expeditiously converting a nation's fishing boats and fishermen to military assets. England used trawlers to maintain control of seaward approaches to major harbors. No one knew these waters as well as local fishermen, and the trawler was the ship type these fishermen understood and could operate effectively without further instruction. The Royal Navy maintained a small inventory of trawlers in peacetime, but requisitioned much larger numbers of civilian trawlers in wartime. The larger and newer trawlers and whalers were converted for antisubmarine use and the older and smaller trawlers were converted to minesweepers

In the aftermath of the First World War, the Belgian Corps de Marine purchased several British war surplus naval trawlers. They were operational during the Battle of Belgium (1940) and one of them, A4, evacuated a large quantity of the National Bank's gold reserves to Britain shortly before Belgium's surrender.

As with Portugal, the RN had a number of trawler-type warships on order from Brazilian shipyards. With the declaration of war by Brazil against Germany in 1942 these vessels were transferred to the Brazilian Navy for anti-submarine and escort duties.

...
Wikipedia