The first submarines surfaced (excuse the pun) during or around the American Civil War. The question I have comes in a few parts:
Did the submarines seen in the American Civil War prompt any change in tactics for surface ships to counter them?
What was the first "modern" military submarine? and what effect did it have on military thinking at the time?
The while the first ship to have been sunk by a submarine was the USS Housatonic, the submarine in question was, understandably, extremely basic. When was the first successful attack by "modern"* submarine sunk? and what ship was attacked?
Finally, when originally inventing the submarine was there an aim other than gaining military advantage?
*Modern = motorized, with powered torpedoes etc.