When Cmdr. Ritchie spills the coffee on his shirt, he is seen at the mess table in PT 109's forward crew's quarters, but when he emerges on deck to see what has happened, he comes up through a hatch at the stern of the boat under the 20mm gun. This hatch is to the lazarette, a small workroom to the rear of the engine room. Ritchie would have had to (quite needlessly) pass through almost the entire boat below decks from bow to stern (front to rear) - through the galley, the wardroom, the dayroom, the engine room, and the lazarette - to emerge from that hatch, passing four other hatches to the deck on the way.
Commander Ritchie (James Gregory) is in the galley having a cup of coffee when the ship crashes into a dock, and the coffee spills all over his uniform shirt. When he appears on deck moments later to see what happened, his shirt is dry and spotless.
(at around 50 mins) When Drewitch (Norman Fell) is in the PT engine room during the rescue of U.S. soldiers from the beach, PT 109 is receiving Japanese shore fire on its port (left) side. Drewitch, however, is wounded by a projectile that pierces the boat from the starboard (right) side.
PT 109 is shown rescuing the remnants of a Marine patrol off Choiseul Island while under enemy fire, and when the Marines are being pulled onto the 109, the number "43" can be seen briefly on the front of the cabin, while PT109 is clearly on the side. Possibly the same boat was used for different scenes, and changing the front number was overlooked.
When PT 109 is coming into Rendova, the bow of the boat is coasting in around 10 mph. The next scene shows Ritchie on the afterdeck with the wake showing the engines at full power.
PT 109 is shown rescuing the remnants of a Marine patrol off Choiseul Island while under enemy fire. This rescue actually occurred on November 2, 1943 - 3 months after PT 109 had been rammed and sunk. The rescue was effected by PT 59, a PT which had been converted into a gunboat and was John F. Kennedy's second and last command in the South Pacific.
The natives who assisted the crew of PT 109 are clearly of African descent. In the South Pacific natives would have been Polynesian.
The Australian Coast Watcher pretends to be communicating on a BC654/SCR284 crank generator powered radio. The generator is present but the "radio" is a SB71 field-phone switchboard.
Unmodified (except for paint) American AT-6 trainers are used to represent Japanese aircraft.
The cylindrical smoke generators on the sterns of the re-created PT boats face the wrong way. Real PT boats' generators were installed with the smoke-emitting nozzle to port (left). The movie boats' nozzles are on the starboard (right) sides of the generators.
Although it is true that African-American sailors served as mess stewards and stevedores during the war, this did not necessarily exclude these sailors from assignment to a gun crew during general quarters aboard ship or ashore, or manning the guns when the assigned crew were killed or wounded. In those days, all sailors, regardless of rate, received basic gunnery training in boot camp.
In at least one scene, there is an airplane contrail in the background. Contrails are created by propeller-driven aircraft as easily as by jets, as a function of altitude and air temperature.
When Kennedy carries Pappy out of the water after swimming to the first island, it can be seen that he walks on a the plank in the water. The plank is there so the actor could avoid stepping on the coral. Later, Kennedy swims out, and there is no plank in the water; he can be seen flinching as he walks on the coral.
When Cmdr. Richie comes to the PT 109 to inspect it, he arrives in a Jeep; when he comes to the PT 109 to be taken to the new base, he arrives in a Jeep. It is the same shot in both scenes. (The duffel bag in both scenes is the telltale.)
(at around 40 mins) There is a shot of PT 109's fuel gauges and other instruments. They were labeled with embossed labels, sometimes known as "Dymo labels", from the company that was known for making the tools and embossing tapes. The scene took place in 1943, but embossing tapes weren't invented until 1958.
Several American flags, in long shot, are 50-star flags (48 in 1943).
The Jeeps seen on Rendova are the CJ-2 model that did not go into production until 1945.
When Ritchie shoots down the Japanese plane, a smoke generator can be seen hooked onto the middle part of the wing. There is nothing there that would generate smoke if it actually had been hit by gunfire. (The plane may explode or catch fire due to the gasoline in the wing, but it wouldn't just smoke.)
On at least three patrols, all of which are supposed to be to different islands, they have exactly the same island layout in the background. Possibly it is even the same take, repeated.
Twice in the film, Lt. (J.G.) Kennedy is asked what time it is, and he responds with "quarter to two" and "two o'clock". A Naval officer would always answer in military time to another sailor. He should have said "1345" and "1400".
When Tiger Tail Leader is granted permission to use Blackett Strait instead of Ferguson Passage to "return home", he ends the communication with "over and out." This is incorrect, as "over" means a response is expected. He should have simply said "out". (Compare to earlier when Blue Jay reports from the plane that wreckage has been spotted in the channel but no survivors are seen. He ends his communication to Oak Leaf 1 with "out.")
The native canoers had no training as evidence by their constantly switching their paddles from right to left.