In early 1917, German submarines were sinking one in every four ships that sailed from British ports. German leaders were confident that they could minimize the U.S.’s contribution to the Allies by preventing supplies and troops from crossing the Atlantic.
The U.S. Navy had a sizable fleet, and was building more ships. However, it lacked the smaller vessels needed to fight submarines and to escort merchant ships, and was undermanned.
It quickly shifted its ship building program to focus on destroyers and submarine chasers. The U.S. declaration of war automatically placed the Coast Guard under Navy command, expanding its ranks. Also, since the Army had priority for manpower, the Navy expanded its recruiting to include women in support roles, freeing up more men for sea duty.
To combat the submarine threat, the British and U.S. started grouping merchant ships in convoys and protecting them with escorts. Submarine sinkings dropped dramatically.
The U.S. Navy helped ensure that tens of millions of tons of supplies reached Europe. Two million U.S. troops safely crossed the Atlantic; only 637 were lost to German submarines. 431 sailors and coast guardsmen were killed and 819 wounded in carrying out this vital duty.