American 18 inch torpedo
There have been a number of 18 inch torpedoes in service with the United States.  These have been used on ships and submarines of the US Navy.  American "18 inch" torpedoes were actually  in diameter, beginning with the "Fiume" Whitehead torpedo of 1890.

Ship classes that carried 18 inch torpedoes include:

Aylwin-class destroyers
B-class through some R-class submarines
Bainbridge-class destroyers
Cassin-class destroyers
Cincinnati-class cruisers
Columbia-class cruisers
Illinois-class battleships
Indiana-class battleships
Kearsarge-class battleships
Maine-class battleships
Montgomery-class cruisers
Paulding-class destroyers
Pennsylvania-class cruisers
Plunger-class submarines
Smith-class destroyers
Truxtun-class destroyers