In Operation Guidance during mid-April 1944, HMS X24 (Lieutenant M H Shean) was towed by the HMS SCEPTRE to Bergen, Norway, to make an attack on a large strategically important floating dock. X24 successfully penetrated the fjords to reach the harbour, but inadequate intelligence caused him to lay the explosive charges under the 7800-ton German merchant ship Barenfels, instead of the floating dock. Barenfels was sunk in the resultant explosion while the floating dock was undamaged. Despite this it was a model attack, and 24 hours later, sick and suffering from headaches caused by the stale air in the boat, Shean and his crew rendezvoused at sea with SCEPTRE for the tow home. Lieutenant Shean was awarded a Distinguished Service Order ‘for great courage, skill and determination in a most hazardous enterprise’.

In September 1944, X24 carried out a further attack on a floating dock at Bergen, this time successful. Once again towed to the area by the HMS SCEPTRE, X24 (Lieutenant H P Westmacott) slipped through 30 miles of islands offshore and a minefield and into a fjord to sail at periscope depth to the harbour. After diving to 35 feet to avoid collision with a merchant ship, Westmacott attached delayed-action charges to the target and escaped. X24 laid two mines under the dock, which broke it in two and damaged two ships moored alongside.

Unfortunately, in the latter stages of the tow to the target, Sub Lieutenant Purdy was washed overboard and lost. Two months later, Leading Stoker Brammer was lost as the diver during a training exercise.

X24 is preserved at the Royal Navy Submarine Museum in Gosport and there is an excellent video explaining the design and achievements of X Craft, including X24.