The United States E class submarines were used as coastal and harbor

Harbor

A harbor or harbour , or haven, is a place where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use. Harbors can be natural or artificial...

 defense submarines prior to World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. When hostilities broke out, the E class were used as training boats.

The submarines of this class were the first diesel-powered submarine. They were known as "pig boats", or "boats", due to foul living quarters and unusual hull shape.

The E class was also used to test and evaluate tactics and new equipment.

The E class was quickly overtaken by newer long range, ocean going submarines. The class was decommissioned in 1922 to comply with the Washington naval treaty

Washington Naval Treaty

The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...

.