On 1 February 1917, the Germans made a declaration that their U-boat submarines were now unrestricted, meaning that Allied merchant ships, neutral traffic and passenger ships in the North Sea and Atlantic ‘war zone’ around Great Britain would be sunk without warning. They gambled that it would speed them to victory and the war would be over by the time an alienated US, who had demanded restricted U-boat warfare, entered the war. Germany had 46 large deep-water submarines and 23 U-boats that could operate as surface vessels. Between February and April 1917, U-boats sank more than 500 merchant ships and by late April an average of 13 ships were being sunk per day. In June 1917, transatlantic naval convoys began to escort groups of merchant ships, causing the monthly losses to drop. The gross tonnage lost in 1917 was still high, at 6 million.
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