Underseaboats.
U-boats
The submarines were either called "submarines" or "U-boats." The German submarine was called the "U-boat"
The name U-boat was applied to German submarines.
Yes, German submarines were very effective in both world wars. The Germans built excellent submarines and still do.
Atlantic Ocean.
Wolfpack
A German submarine used in WW I was called a U-boat.
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Well, only the Germans called their submarines U-Boats, this was short for the german word unterseeboot which means submarine.
Submarines, commerce raiding.
U-boats. (German submarines)
Oilers then merchantmen.
German U-Boats are submarines. In World War 2, the Germans used these submarines to attack in groups of three or more. The Germans called these groups of submarines "wolfpacks". The Americans, British & Canadians also used the name "wolfpack" to refer to a group of German U-Boats.