PT Boats were at one time looked down on by the regular blue water Navy being that they were smaller, wooden hulled craft not built for large ocean voyages in all weather conditions, lacked serious armor and armament and were more of an "escort" type craft. As the war went on and more and more of these smaller, faster and more agile craft were introduced their usefulness in bottle necked waterways around the islands that the US and Japan fought over. Their speed, agility, flexibility and shallow draft made them ideal for not only taking it to the Japanese fleet with their torpedoes, but also being used to infiltrate beaches with Marine Raiders and the like...they were doing black ops for the Navy before black ops were cool.
What is often over looked about Ernest Borgnine is that he was, in fact, an actual Navy veteran of WWII, serving aboard destroyers for 10 years between 1935 and 1945. That's Pretty cool.
A character to the end, Borgnine made the net a few years ago for this little quip about what he does when he's alone....I love the guy on the show "I just shook his hand!"