PT boat stands for what?

Answer 1

The designation PT stood for 'PATROL TORPEDO". These boats were relatively small and maneuverable as patrol boats but could pack a big punch if necessary, by launching their deck mounted torpedoes at large enemy craft.

Perhaps the most famous of these boats was the PT 109, the boat that John Fitzgerald Kennedy, later President of the United States, was assigned to in WWII. The boat was run down by an enemy ship, Kennedy and the other crew were in the water for some time before being rescued. See that story elsewhere.