Simplify the following text for a Grade 6 native English-speaking person.
Original: PT Boats were a variety of motor torpedo boat ( hull classification symbol `` PT '' , for `` Patrol Torpedo '' ) , a small , fast vessel used by the United States Navy in World War II to attack larger surface ships .
Simplified: PT Boats were motor torpedo boats ( `` PT '' , for `` Patrol Torpedo '' ) . They were small , fast ships used by the United States Navy in World War II to attack larger surface ships .