On 7 June 1917, the PARGUST was attacked in the Atlantic Ocean by the German submarine UC 29. During the attack the gun covers came loose and William Williams volunteered to stay behind to hold the covers in place by hand so as not to reveal the weapons too early. The decoy crew disembarked the ship on lifeboats, upon seeing this, UC 29 surfaced and approached the ship. When the U-boat got within 50 feet, Williams dropped the covers and the guns fired. UC 29 was sunk with 23 hands on board.

Source: Henry Newbolt, Submarine and Anti-Submarine (1919).