Operating in the open sea and sinking vessels. All that was required of them.
Why don't you just Google "World War 1 Submarines?"
Submarines were sometimes referred to as submersibles.
1, 200,000 Soldiers 30 Warships 11 Submarines.
Steel plates.
Atlantic Ocean.
2,200,000 Soldiers 97 Warships 40 Submarines.
Yes, German submarines were very effective in both world wars. The Germans built excellent submarines and still do.
The US helped France in world war 1 with submarines in the Atlantic.
Yes, many submarines were used in WW1 by most of the major combatants.
World War 1
U-boats=Submarines
Before the war, people mainly used ships and boats, therefore, the people with the submarine could destroy these ships.