Final answer:
Germany used submarines as their secret weapon to cut off British supplies during World War I.
Step-by-step explanation:
Germany used submarines as their secret weapon to cut off British supplies during World War I. The German government declared the sea-lanes leading to Europe and France as war zones and warned Americans that any ship heading towards these ports would be sunk. Germany had developed effective submarines and torpedoes, and their naval strategy involved sinking incoming supply ships to blockade Great Britain and France.