HMS C33 (Lt G E B Carter) had been operating with the armed trawler Malta off the Norfolk coast and the exact cause of her loss is unknown. She detached from her trawler escort at 2015 on 4 August in order to return to harbour. Nothing further was heard except a few wireless signals indicating she had nothing significant to report. These transmissions ceased at 2150. As there was no German claim of an attack on C33, it is possible that she struck a mine near Smith’s Knoll while returning to base on 5 August 1915.