Answer: German attack of American Merchant ships
Explanation: When the German submarines began to launch attacks again. The first ship to be hit by a torpedo by a German U boat was U-30 , on May 1, 1915, resulting in 3 killed, which wasnt enough to launch a full war effort. But the second ship to be hit was a passenger ship called the Lusitania, which was actually a British ship. This ship was hit 6 days after the Merchant ship and resulted in the death of 128 civilian lives. About 1,198 people perished overall in the attacks of the German U boat attacks. When America began to rally to begin their assault, hundreds of Merchant ships had been sunk already, another reason why America joined the war effort, to protect their economy. As these sinking if were to continue would have a heavy impact on each economy.