A submarine operating in hostile territory never 'pings', or uses its active sonar. The pings can be picked up by enemy submarines and surface ships and homed in on, similar to calling out or making other noise on land.
When Gable and Warden are playing sink "Bungo Pete" in Gable's office, a model battleship is on Gable's desk. This was obviously a Revell kit, likely a model of the USS Missouri, that dates from the mid 50's.
In the early part of the film where Lancaster meets Gable, who is pruning a tree, in the background you see the same half dozen cars driving back and forth constantly.
Amongst the vehicles appears to be a '49 Buick convertible.
At the end of the film when the torpedoes travel towards the Japanese sub, from the sub's point of view, the decoy is forward of the sub, so the torpedoes pass behind it. However, from the US sub's point of view, the decoy is still between both subs when the torpedoes pass underneath it.
Torpedo tubes on submarines are numbered odd on the port side and even on the starboard side. When they fire #1, it comes out the starboard side from # 2 tube. In fact, all the shots come out of the same tube.
In the first attack in the opening scenes the range to the target is given verbally as 1,500 yards. The range to target on the TDC (Torpedo Data Computer, an electromechanical analog computer) is shown a few seconds later as 4,400 yards.
At approximately 1 hour and 17 minutes, the submarine breaches the surface at a steep angle. The periscope is fully 90 degrees to the surface of the water. The submarine begins to level off and the periscope does not change angle.
In the protracted scene between Capt Richardson and Mueller where Mueller is on report, Richardson pulls out a pack of cigarettes and lights one. The next several close up shots of him do not show him with a cigarette, he is playing with a model of a ship, or smoke from a lit cigarette. Near the end of the scene we see smoke from the cigarette rising.
At the end where the American sub shoots torpedoes at the Japanese sub, the camera shows the view from the Japanese sub with torpedoes incoming. There is no sign of the American sub anyplace in the distance even though they are still on the surface when the torpedoes hit the target.
In the opening shot on the Nerka, Mr. Bledsoe is in the control room and exits through the door to the forward battery compartment. In the next shot he is entering the after battery compartment which is the opposite way.
After Bledsoe has explained to the crew that their orders would not take them to the Bungo Straits, he goes down a ladder. The next shot shows him where he landed at the foot of the ladder, but the ladder itself has vanished.
In the underwater scene after Commander Richardson orders the bodies to be ejected with the rest of the 'oil slick', 2 depth charges sink past the submarine. At the conning tower, one of the depth charges has an explosion, yet the depth charges continue to sink and ultimately detonate below the submarine.
When the Akikazi is attacked for the last time, during the "binocular" view scene the Akikazi tracks from center line to the starboard (right) side, but from the conning tower Lt. Bledsloe is clearly looking straight over the bow and shows no movement.
A depth charge is seen rolling off the sub's deck and exploding directly under the keel. And later, three depth charges explode one after the other, all around the stern of the boat.
A depth charge exploding that close under the middle of the keel would have broken the sub's back and sent it to the bottom, let alone three close in nearly simultaneous detonations. These images were meant to build tension, but are totally unrealistic.
After getting a report that the hatch had been secured with block and tackle, Cmdr. Richardson loses his balance and grabs the block and tackle apparatus. When he does this, the rope is nowhere near tight enough to secure anything. He moves the ropes around a few times with his fingers. In reality, those ropes would be as tight as fiddle strings. They would be very very taut and would be like a solid rod.
The Japanese destroyer classes "Akikaze" and "Momo" do not exist. The destroyer "Akikaze" was an old (1919) "Minekaze class" destroyer, and the "Momo" a "Matsu class"... , but the first one of them was launched in 1944, a year after sinking it in the movie.
During the sequence where the submarine comes under Japanese air attack the one shot we have that shows the Japanese planes up-close is clearly stock footage of the American SDB Dauntless dive bomber, to the point that the American insignia have been obviously airbrushed out.
During the time Cmdr. Richardson is bedridden, when the sub fires torpedoes no movement of the boat is seen, even though all the previous times a torpedo was fired, the whole boat moved. Cmdr. Richardson's stateroom should have been seen to shudder when the torpedoes were fired.
In the opening scene of the film, Gable's sub is located off the Bungo Strait, near the coast of Japan, in 1942. After his sub is sunk, the survivors are shown floating in the water, the movie goes to opening credits, and the next scene is of Gable sitting in his office at Pearl Harbor. One must assume that they were rescued by friendly vessels and returned home. In fact, any sub sunk that close to Japan at that time would have never been within rescue range of an American surface ship to be picked up. American surface ships would have been sitting ducks for the home waters defense forces of Japan. The US Navy only got into that area much later in the war, in spring of 1945 or so, after the Japanese navy and air force had been effectively neutralized. Even another sub would have found it difficult to rescue the crew before they were picked up and sent to a POW camp. In short, this opening sequence is bogus in terms of reality, but needed as a plot line for the rest of the movie.
At various times they shoot torpedoes, all from the forward tubes, saying, "fire one," "fire two," "fire three," "fire four," "fire five" or "fire six," but from the underwater camera shots, the submarine clearly has only four forward tubes, not six.
Near the end of the film, when they finally realize that there is a Japanese submarine nearby shooting torpedoes at them, the first time we see inside the Japanese sub, a close-up of its periscope shows that it has an air outlet plug marked "air-out." (There are drying inlet and outlet plugs on periscopes that are used during maintenance to force dry nitrogen through the mechanism to dry out the interior of the periscope.) It's a Japanese sub, so the words would not be in English.
When Lt. Jim Bledsoe decides to return to the Bungo Straits towards the end of the film (at around 1h 15 mins), the submarine does a U-turn. As it does this you can clearly see what appears to be an American aircraft carrier in the distance on the horizon.
During the first torpedo attack on the way to the Bungo Suido, the attack setup is described as one freighter with one destroyer escort. However, when the freighter is torpedoed, a third ship is visible in the shot.