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.