HMS Powderham was one of 93 ships of the of inshore minesweepers

Minesweeper (ship)

A minesweeper is a small naval warship designed to counter the threat posed by naval mines. Minesweepers generally detect then neutralize mines in advance of other naval operations.-History:...

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Their names were all chosen from villages ending in -ham. The minesweeper was named after Powderham in Devon

Devon

Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...

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In 1960 she was selected to be converted to an inshore survey vessel and was re-named HMS Waterwitch. For a while she was manned by civilian Port Auxiliary Service

Admiralty Yard Craft Service

The Admiralty Yard Craft Service was the civilian service which operated auxiliary vessels for the British Admiralty, mainly in HM Dockyards or the vicinity. It was renamed the Port Auxiliary Service between 1960 and 1962, and later the Royal Maritime Auxiliary Service after 1970.The service...

personnel and was named MV Waterwitch.