HMS Powderham was one of 93 ships of the Ham-class of inshore minesweepers. Their names were all chosen from villages ending in -ham. The minesweeper was named after Powderham in Devon. In 1960 she was selected to be converted to an inshore survey vessel and was renamed HMS Waterwitch. For a while she was manned by civilian Port Auxiliary Service personnel and was named PAS Waterwitch.