Between 1915 and the entry of the United States into the war in 1917, merchant shipping was badly shaken by German submarines. In 1915 losses were exceeding the replacement rate of ships, and Britain's supply lines were seriously threatened. There was a brief respite when unrestricted submarine warfare was suspended following the sinking of the Lusitania. However, shipping losses were still high and the Kaiser agreed to allow the submarines to return to unrestricted attacks in 1917. Only the entry of the US in 1917 and the pursuit of a convoy system, saved the British supply lines from total strangulation.Cobh played a crucial and largely forgotten role in this battle for the Atlantic. It was from its secure harbour that British and American naval forces battled the German empire's submarines and navy. In this new and comprehensive study of the role Cobh played, Liam Nolan looks at the circumstances that surrounded the feat and at the interesting characters who commanded the navies and crewed the ships.