HMS Moonstone was an armed trawler of the Royal Navy employed in anti-submarine warfare duties during the Second World War.

In June 1940 Italy joined the war against the Allies, and the Royal Navy commenced operations against the Regia Marina.

On 16 June Moonstone rescued the crew of the Norwegian tanker James Stove which had been sunk by the Italian submarine Galileo Galilei earlier that day.

The submarine's captain, realizing his opponent was smaller and less heavily armed, and troubled by an escape of poisonous fumes in the boat, chose to fight on the surface, where he would still have the advantage.

For this effort Moonstone's skipper, bosun William Moorman, was awarded the DSC and referred for an officer's commission.