What was the first intended use of the submarine?

During the American Revolution, the Colonists tried to use a submarine called The Turtle to sink a British warship in New York harbor. The English ship had a metal plate attached to it, and the attack failed.

During the USA civil war, the South, (Confederate States), tried to use submarines to break the Union blockade, but, although they sank one Northern ship, the sub also sank, and it was not worth the effort.

The German use of submarines in WWI, was the first time a country made an effective use of the boats, and from then on, many countries with navies tried to get submarines in the fleet.