How the Royal Navy assembled its wartime trawler force

Were the trawlers mentioned in the lecture requisitioned at the start of the war or already commissioned?

Most were requisitioned, while some were purpose-built during the war and later sold for civilian trawling.

Most of the trawler force came from requisitioned vessels. Some ships were newly built during the war to naval-trawler standards. Those purpose-built ships could then be sold into ordinary fishing service after the war. The force therefore combined civilian hulls taken up for naval use with naval construction that later entered commercial work.