The submarine started as an important way to isolate England from supply convoys. As a submarine could slip up on a convoy unseen and launch a torpedo it also had a similar effect as the modern day sniper, causing fear among the ships not hit.
As Anti-Submarine Warfare was more and more successful the submarine lost it's value.
During the Cold War its importance was to resurge as a platform to launch nuclear missiles and to hunt the large missile subs or Boomers as they were called. There are some who have gone as far as to attribute the fact that there was never a nuclear exchange between the USA and the USSR to the fact that each side knew that the submarines would launch a counter-strike.
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