On 13 November 1939, at 05.25, "Adventure" was badly damaged near the Tongue Light Vessel, in the Thames Estuary by an underwater explosion. 23 of her crew were killed or fatally injured. The bridge was wrecked and crew and fittings were thrown against bulkheads and down hatchways with lethal effect. She was successfully taken in tow to the Medway by tugs from Ramsgate, and later repaired at Chatham Dockyard. She had been en route from Grimsby to Portsmouth, and escorted by the Harwich-based destroyers and . "Blanche" was also mined at 08:10 and sank with the loss of one man. Originally floating mines were blamed, but it soon transpired that magnetic mines laid by German destroyers a few hours before were responsible. "Adventure" returned to service in October 1940.