Factual error: It is barely credible that a young Victorian woman like Elena would even think about wearing a goatskin miniskirt - exposing her legs in those days would be akin to walking about topless nowadays. Even if she did those bright yellow cotton knickers - gleefully visible in the scene in the beehive - are in no way from the 1860s. Her pants are a hundred years ahead of their time.
Plot hole: The huge guns are set high up on a cliff face facing out to sea and it is obvious that they cannot be depressed to fire at a downward angle - the massive gun carriages set on rails would prevent that happening. They cannot be elevated to fire at an upward angle, too, because they fit pretty snugly in the hole cut into the cliff face to accommodate them. This means that their maximum and minimum ranges would be quite close together, covering a strip of maybe a few hundred metres either side. Given that the sea is completely open on the side of the island they are protecting, why don't the ships targeted by the guns while passing the island simply sail inside or outside of the narrow stretch of sea the guns can hit?
Continuity mistake: The shots are badly mismatched when Demetrius saves the elderly slave about to fall from the rope. Their arms and legs shift positions multiple times between takes.
Continuity mistake: In the park, when Pongo tries to get Roger to meet Anita he yanks Roger ahead, and Roger leaves his hat on the bench. In the next shot, when Roger and Anita are entwined in Pongo's leash, Roger is wearing his hat. (00:09:30)
Factual error: The rifles that Jake Cutter has Paul Regret dig up are Henry repeaters, or possibly 1866 Winchesters. Either way weapons unavailable in the period depicted in the movie.
Factual error: With the radiation belt on fire, the icecaps begin to melt. The Seaview is bombarded by huge chucks of ice. The ice is sinking to the bottom like stones. Ice floats, it doesn't sink.
Revealing mistake: At the opening of the film as the pirate ship passes left to right the flags are blowing in the opposite direction of the ship's movement and the sails keep blowing back although the ship keeps moving forward. Notice the large amount of churning water at the ship's rudder indicating that the boat is powered by a motor.
Other mistake: When the parent monster is just about to enter Piccadilly square, for a brief moment a view of a bus is shown. The writing on the bus is reversed.
Revealing mistake: At the beginning of the movie, Talua is depicted as an isolated island in the South Pacific. Several shots show other islands in the movie. Many segments were shot in Hawaii (Maui) and you could see the Island of Hawaii in the distance.
Revealing mistake: The Son of Hercules brings to the nearby village the old man that died on the beach. You can see the 'corpse' move his arm to assist Mark Forest as he dismounts him from the horse.
Other mistake: Brian Keith sneaks into an Indian encampment at night while they are sleeping. In order to stampede their horses, he rapidly fires the one and only six-shooter revolver he has into the air...eight times.
Suggested correction: The guns are firing across a strait. A strait is a "narrow passage." Since the targets must appear at a limited range, the guns only need a limited elevation angle.
Noman ★
Watch the film again. The guns are facing the open sea. There is no land visible anywhere behind the ships. If that's a strait, it's a very, very wide one.
The mission given says the guns are guarding a strait. The last shot of the six destroyers shows land behind them on the opposite side of the strait.
Noman ★
Other summaries explain that the strait is only deep enough for the ships at the place which matches the guns' range. So ships could not take advantage of further away or closer in.
Then what are the dark shapes rising out of the sea on the far side of the ships. If they are not islands, what are they?
Noman ★
Suggested correction: That the gun carriages are supposedly set on rails is not correct. In the novel template, as well as in the film, it is shown that the guns were installed on turntables. And as for their variable angles of fire - it could be due to (fictional) modifications.
Daniel4646