This book examines the history of the German Type XIV submarine tankers, better known as the "Milk Cows", which played a crucial logistical role in sustaining long-range U-boat operations during the Second World War. Designed to refuel and resupply combat submarines at sea, these specialised vessels significantly extended the operational reach of the German submarine fleet in the Atlantic. John F. White traces the development, deployment and operational careers of the Milk Cows from their introduction in 1941 until their destruction by Allied forces. The book details the complex refuelling operations conducted in remote ocean areas and explains how Allied codebreaking and improved anti-submarine warfare gradually turned these valuable support vessels into prime targets. As the war progressed, the loss of the Milk Cows severely reduced the effectiveness of Germany's U-boat campaign. Drawing on extensive research and wartime records, the author provides a detailed account of a little-known but strategically important aspect of the Battle of the Atlantic, illustrating how logistics and supply networks could influence the outcome of naval warfare. (AI-generated content description)