U-boats were not yet used in World War 1. U-boats were invented for use during WW2.
'U-boats' was the name given to German submarines in both the first and second world war.
The Germans manufactured the u-boats.
375 German U boats were commissioned during WW 1.
They had over 1,000 U-Boats They had over 1,000 U-Boats
Sinking merchant ships.