Hindenburg and Ludendorff forced a return to the policy of unrestricted submarine warfare on 9 January 1917 and engineered the dismissal of the Chancellor Bethmann-Hollweg and other opponents of the policy the next day. The policy was to resume on 1 February, to sink of shipping per month and knock Britain out of the war in five to twelve months. Optimistic claims by the navy were less important to the decision than the "desperate" position of the western armies and the decrepitude of Germany's allies. Another front in the west was to be opened by the resumption of air attacks on Britain. New aircraft had become available to replace airships, which had become too vulnerable to British counter-measures in 1916. Planning began in late 1916 and Operation Turk's Cross () began in May 1917.