From the very outset of war Nazi Germany demonstrated its determination and ability to lay siege to the British Isles by the laying of mines in shipping lanes. Losses to both merchant ships and naval vessels became a serious factor. If supplies continued to be lost by a combination of U-Boat and mine attacks the very survival of the nation was at risk. Finding counter-measures to the German mine offensive was thus a top priority. The responsibility for this vital work rested with a small group of highly skilled and courageous naval specialists based at HMS Vernon, the RN’s mine and torpedo shore-base at Portsmouth. Ranged against them was a growing and ingenious array of weapons: magnetic, acoustic, oyster, booby-trap mines to name but four varieties. Some were laid by boat, others dropped from the air. The story of HMS Vernon’s contribution led by men such as Commander JGD Ouvry DSO and Captain R L Lewis DSO and many other courageous figures has been written by John Frayn Turner, the distinguished historian who served with them.He adopts a fast moving style to describe the near continuous struggle to detect, understand and master the best efforts of the German war machine. He brings home the constant deadly danger faced by these highly skilled and dedicated men.