Of this number 473 were in the Mediterranean, 824 were in the English Channel between The Nore and Falmouth, 557 were in Irish waters or on the west coast of England, and the remaining 1,230 were on the east coast of England and the east and west coasts of Scotland and the Orkneys and Shetlands.
The work of these vessels was almost entirely of an anti-submarine or minesweeping nature.
The trawlers were engaged in patrol duty, convoy escort service, and minesweeping.

The drifters worked drifting nets fitted with mines as an anti-submarine weapon, and also in the case of the Dover area they laid and kept efficient a barrage of mine nets off the Belgian coast.

Some were also fitted with hydrophones and formed hunting flotillas, and some were engaged in minesweeping duties, or in patrolling swept channels.

At Fleet bases a small number were required to attend on the ships of the Fleet, and to assist in the work of the base.

The whalers, being faster vessels than the trawlers, were mostly engaged on escort duty or on patrol.