Answer: Germany was stepping up its efforts to stop goods from reaching the Allies.
Step-by-step explanation:
After the Lusitania incident in 1915, Germany had pledged to stop unrestricted submarine warfare. They made that pledge to keep the USA from entering the war st that time. But by 1917 Germany went on the offense with submarines again, hoping to end the war and win. However, this was one of the factors that pulled the USA into the war, and Germany lost.