THEY called it Liverpool's finest hour and greatest sacrifice. When France fell in the spring of 1940, it was a 22-mile stretch of water which helped to save Britain from invasion. It was left to the courageous merchant seamen, and the navies who protected them, to keep open those channels to the Americas, Africa and beyond. The Battle of the Atlantic saw six long years of conflict - and Liverpool was at the heart of it. Now, in May 2013, the country is once again turning to the city as it plays a major role in the 70th anniversary commemoration of the conflict. The Mersey was the main gateway to Britain for millions of tons of food and war materials, and an essential naval repair base. And Liverpool offered a friendly face for thousands of sailors who poured in on shore leave. All this made the city a key target, and we paid the price, enduring months of sustained bombing. On February 7, 1941, Western Approaches Command was divided and its headquarters was moved from Plymouth to Derby House, Liverpool. The headquarters of the RAF's Coastal Command moved to Liverpool at the same time. As Liverpudlians went about their lives above ground, far beneath the paving stones the command centre of the Battle of the Atlantic was a hive of activity. Admiral Max Horton, took over as commander-in-chief in 1942 - his leadership, with submarine hunter Captain Johnny Walker, played a vital role in the defeat of the U-boat. From Western Approaches HQ, they planned the hunting and eventual sinking of the notorious Bismarck and other enemy surface raiders and blockade runners. The Battle of the Atlantic was pivotal to the success of the allied war. The Germans never really understood why, by May 1943, the tide had turned. Featuring stunning images and rare stories from the archives, this special 70th anniversary publication, priced GBP4.99, tells the city's own secret story of the longest and hardest won campaign of the Second World War. This is an 84 page special edition magazine.