An operation to recover the biggest ever cargo of silver sunk at sea led to the discovery of a unique set of letters posted but never delivered in 1940.

Those letters, which are now on show, are the inspiration for a piece of interactive children’s theatre.

On 16 February 1941 the British India Steam Navigation Co cargoship Gairsoppa, carrying 2,817 silver ingots weighing 109 tons, was sunk by a German U-boat in the Atlantic Ocean 300 miles (480km) southwest of Ireland.