In the earliest days of submarine warfare, they were considered a dishonorable form of warfighting - that is, until the the honorable Navies of the world started getting their ships sunk, and finally realized the full potential of submarine warfare.
One of the provisions in the Treaty of Versailles which ended WWI was that Germany turn over all of her submarine technology to the Allies and stop building them. Hitler of course developed and built them in secret.
Unrestricted Submarine Warfare in WWI had its political backlashes, but by WW2, those worries were gone. It is similar to how snipers were originally thought of (and even today some consider sniping a dishonorable way to fight), but the psychological impact of both submarines and snipers, and the amount of resources that are used to track and destroy them, make it certain that they are a force to be reckoned with.
Any belief in those times that submarine warfare was dishonorable is history; they are considered the front lines of the Navy, often going to places before anyone else, undetected, where they can gather Intel or insert covert operations teams.
Germany practiced unrestricted submarine warfare.
Well, there is no "The" underwater warfare, but there is underwater warfare. Underwater warfare is battle or warfare that takes place under the ocean, like in a submarine.
"Guerre de Course"; Commerce Raiding.
Unrestricted Submarine Warfare.
Germany's return to unrestricted submarine warfare.
Enemy surface ships are the main target of submarine warfare
Germany hoped that submarine warfare would lead to war.
Anti submarine warfare
Germany's submarine warfare was unrestricted. These attacks led to World War I.
USA
submarine warfare
Submarine warfare has existed since the early 1900's, and continues to this day. Though the last ship sinking by a submarine was in the Falklands War, the evolving missions of submarines have taken submarine warfare well beyond just sinking ships and submarines.
unrestricted submarine warfare
Germany's unrestricted submarine warfare
Anti-Submarine Warfare.
it was Germany.
The Sea people