The open end of the Algarve Inland Sea required patrolling to stop pirates/smugglers from escaping without paying the Government Taxes on exports. Namely precious metals and gems. The old destroyers from WW1 had been doing the job but as they got older and more unreliable a new replacement type was sought. Much smaller and just as heavily armed the new patrol craft became a success with their type being used all over the world. From fighting E-boats in the Channel and aircraft around the coast of England, to being heavily involved in the Mediterranean fighting Italian cruisers, destroyers, aircraft, and German tanks along the coastal roads of North Africa. Eventually hundreds were produced and built by Algarve, Australia, Britain, Canada, and other Commonwealth countries. The version below is one of the 1940 built units that went to the Mediterranean.
