Peter Fonda, who resembled the young JFK in build and looks, was also considered for the role of PT 109's last skipper as were both Roger Smith and Ed "Kookie" Byrnes (See: Edd Byrnes) from the popular TV series 77 Sunset Strip
In the film, PT 109 is Navy gray in color, but the real boat was actually painted dark green when JFK commanded her - to camouflage it when moored along the bushes of the shoreline during daylight.
It was decided and approved by President Kennedy that 'Cliff Robertson' speak in his natural voice and not try to imitate JFK's Boston accent for the film.
The boats were actually 85-foot long Air Sea Rescue boats. The cockpits were rebuilt to scale because the boats were some 5 feet longer in overall length than the Elco PTs.
The meaning of film's title "PT 109" is PT Boat 109 or Patrol Torpedo Boat 109 or Motor Torpedo Boat PT-109. PT is a symbol referring to a motor torpedo boat's hull classification symbol (aka hull codes aka hull numbers), in this case PT stands for Patrol Torpedo. Occasionally, movies will lend their titles to the numerical designation of a boat (See also: U-571).
The real PT 109 had been engaged in continual combat for five months when JFK took command, but was not the derelict, inoperative hulk depicted in the movie.
When President Kennedy saw early footage of parts of the film, his only complaint was that 'Cliff Robertson' was parting his hair on the right, while JFK's hair parted on the left. Robertson dutifully parted his hair on the left for the film.
WILHELM SCREAM: When the 109 is cut in half, one of the men screams the Wilhelm scream.