title: Submarine warfare
context: The age of submarine warfare began during the American Civil War. The 1860s was a time of many turning points in terms of how naval warfare was fought. Many new types of warships were being developed for use in the United States and Confederate States Navies. Submarine watercraft were among the newly created vessels. The first sinking of an enemy ship by a submarine occurred on 17 February 1864, when the Confederate submarine H. L. Hunley, a privateer sank the sloop USS<i>Housatonic in Charleston Harbor, South Carolina. Shortly afterward, however, H. L. Hunley sank, with the loss of her entire crew of eight.
question: When were submarines introduced in warfare?
answers: The 1860s