U-48 : the most successful U-boat of the Second World War /Franz Kurowski.

Following the signing of the Treaty of Versailles in 1919, Germany was not permitted to build or operate submarines. However, clandestine training took place on Finnish and Spanish submarines and U-boats were still built to German designs in Dutch yards. After the outset of the Second World War, a fleet of U-boats was created in Germany and U-48 took up its place around England. By August 1941, U-48, the most successful boat of the Second World war, had sunk 56 merchant ships.