Stickleback-class submarine
 The Stickleback class submarines were midget submarines of the Royal Navy initially ordered as improved versions of the older XE class submarines. They were designed to allow British defences to practice defending against midget submarines since it was theorised that the Soviets had or could develop such craft.The Royal Navy developed plans to use these craft to carry a 15 kiloton nuclear mine (based around the Red Beard weapon) codenamed Cudgel into Soviet harbours.