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 gr?

Germany submarines were very effective in the sea in helping curb the resupply of the triple entente all during the war.
 the sinking of various merchant ships in the Atlantic by Germany submarines was a major catalyst in the USA decision to join the war, which served as the major reason why the triple alliance especially Germany were defeated.

Starvation, debt, financial downfall.