Since the Germans didn't have such a powerful Navy, what type of weapons were used to sink ships?

Answer: Torpedoes

Explanation: Because that is what they used to sink the U. S ships

Because its navy did not equal the number of ships and the firepower of the British Navy, Germany built a large fleet of U-boats, submarines, which proved lethal and effective against British, American and other allied vessels. Their main weapon was the torpedo, capable of sinking large ships. In both WWI and WWII, German submarines operated mainly in the Atlantic. Their goals were to cut the supply lines of Britain and sink military ships.