The vessels were intended for use as mine-sweepers and for anti-submarine warfare, and the design was based on commercial types, adapted for naval use.

The purpose of the order was to make use of specialist mercantile shipyards to provide vessels for war use by adapting commercial designs to Admiralty specifications.

[1] With the onset of war, Bassett served as the prototype for a series of Admiralty trawlers, of which a total of 180 were built during the conflict using a variety of naming schemes.

[2] Four vessels were built for the Royal Canadian Navy at various yards;[1] these ships had strengthened hulls to cope with pack ice conditions and were also known as the Fundy class.

[3] A total of 50 vessels were ordered from Indian yards (including two for the Ceylon Government)[4] though in the event more than half were cancelled.