What effect did submarines have on World War 1?

Submarines, particularly German U-boats, had a significant impact on World War I by disrupting Allied shipping and trade routes. Their ability to launch surprise attacks on naval and merchant vessels challenged traditional naval warfare and led to severe losses for the Allies. This unrestricted submarine warfare contributed to the United States entering the war in 1917 after several American ships were sunk. Ultimately, submarines changed naval strategy and highlighted the importance of underwater warfare in modern conflicts.