Question

what was the most significant use of german submarines during world war i?
deterring the expansion of the war
submarines were supposed to prevent a ground war in germany.
preventing the resupply of allied forces
reducing overall casualties

Explanation:

During World War I, German U - boats aimed to disrupt the supply lines of the Allied Forces. By preventing the resupply of Allied Forces, they hoped to gain an advantage in the war. Deterring war expansion was not their main use. Submarines could not prevent a ground war in Germany, and they did not aim to reduce overall casualties.

Answer:

preventing the resupply of Allied Forces