The latex make-up on actors Sonny Chiba and Peggy Neal changes from shot to shot, sometimes disappearing altogether.
At minute 08:28 Ken and Jenny are shown close enough to a beach for the waves behind them to start beach rolling (surf), five seconds later with the boat still sitting still they're back outside the surf line.
At 1:01:32 Ken and Jenny have reverted back to laying on the tables despite Ken in a previous scene at 00:55:00 having gotten up and consequently gotten into a fight with another character.
At minute 10:26 Commander Brown is shown wearing a white flat top hat with his beige uniform. Navy regulations do not allow for mixing and matching standard uniforms with dress white uniforms.
The camera Jenny uses and then finally loses in the ocean is not an underwater camera, it's just a standard 35mm camera which was destroyed by taking it into the ocean. Neither the lens or the film advance show any sign of submersion capability.
Comment Jan 2021 - the camera appears to be an early model Nikonos underwater camera.
During one of the fight scenes (after control of the cyborgs is lost) one of the cyborg costumes is clearly torn below the shoulder, exposing the stuntman's skin.
At about 1:04 minutes one of the amphibious creatures falls dead, but as he falls, his fish costume tears at the knee, and reveals a human kneecap.
At 5:0f5 when the Captain orders Fire one", two torpedoes are fired instead, and then two torpedoes are shown traveling side by side.
At 5:05 when the Captain orders "fire one", two torpedoes are fired instead, and then two torpedoes are shown traveling side by side.
The shot of the submarine firing test torpedoes at the beginning of the film and shot of the submarine firing torpedoes at the enemy missiles towards the end of the film are the same.
After Ken says that they are 3000 feet underwater , Jenny proposes that they could escape with their 'aqualungs', to which Ken responds that the oxygen wouldn't last. In reality , at 3000 feet, they are far too deep for SCUBA - the pressure would kill them instantly (the world record for SCUBA (as of 2021) was just over 1000 feet).