a small, fast boat used by the US military forces, especially during World War II. It was used especially for firing torpedoes (=explosive weapons that travel under the sea) at enemy ships. Many Americans remember that President John F. Kennedy fought during World War II in a PT boat, called PT 109, and that when it was sunk, Kennedy led the men to safety.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
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