At a distance, the American sailing ship they attack clearly has no gun ports from which to fire cannons, nor is the sailing ship ever in a position to be able to fire at the airship.
Just before the warship is bombed, Robur observes it through the scope. The view shown of an approaching sailing ship is clearly filmed from sea level. A moment later he looks again and the view is from above.
When the sailor accosts Charles Bronson and his party in their stateroom, his pistol switches positions between shots. In the first shot he is holding the pistol in his right hand and resting it on his left hand, leveled at his waist and in the next shot he is holding the pistol only with the right hand in a raised position, at about chest height. It switches back and forth twice. His position in the doorway also changes between shots.
As Strock and Evans dangle from the Albatross somewhere between Ireland and England, they are dragged over trees and hills, until suddenly they're unaccountably over rock formations in arid land usually found in the American West.
When bombing the British ships, there are four bombs in the rack, but five bombs are dropped.
The Albatross purports to take on water without landing, by dropping a pipe and sucking the water up. If they pulled a perfect vacuum, which is the best they could do when sucking the water, then the theoretical maximum height of the pump above water level would be about 34 feet. In practice it would be less, and it appears that the Albatross was at an elevation that would preclude using this method.
Although the Albatross can fly forwards and can ascend, descend, or hover, it is never explained nor shown how the ship turns. The rudder at the stern of the ship never moves and the many horizontal propellers that support the ship could not turn it.
The amount of wood needed to keep Prudent's balloon aloft would more than fill the gondola and leave no room for passengers.
The shot of the "warship" from sea level is actually Fred MacMurray's ship, the "Gerrymander" from the 1952 film Fair Wind to Java (1953), which was also directed by William Witney for Republic. The same footage was later used on "The Wild Wild West".
Whilst doing repairs after a bombing run and removing the damaged "lifting" blades, one of the crew members is being handed the removed blades. One blade clearly has no hole in it. Previous shots of the top of the Albatross show that the blades are mounted on top of shafts. How could the blade be attached without a hole?
In the control room and Robur's cabin, the views through the windows on either side are inexplicably obscured by opaque colored glass or curtains. However, this is to cover for the shortcomings of a flat rear-screen projection being used.
Robur says that the ship is moving at 150 to 200 mph, which is measured as he says by the wind resistance, but when he's out on the forward deck nobody's blown around by the wind.
While doing repairs after a bombing run and removing the damaged "lifting" blades, one of the crew members is being handed the removed blades. One blade clearly has no hole in it. Previous shots of the top of the Albatross show that the blades are mounted on top of shafts. The blade could not be attached without a hole of some kind.
Many of the scenes of the African battle are seen by Robur from angles clearly impossible from an airship, including several obviously shot from ground level.
The film is set in the 1800s, though as the Albatross flies over London, Robur looks through the scope and sees Elizabethan London, including Shakespeare's Globe Theatre. The shot is stock footage from Henry V (1944). Soon after, more recent London footage appears, including the 19th century Tower Bridge. The aerial view of Paris is definitely 20th century.
Robur's men use single-fire flintlock pistols. Yet the film is set in 1868, three years after the American Civil War, which saw wide use of percussion cap firearms, revolver pistols and repeating rifles, all of which existed before the War. For a man who claims to be ahead of his time, this is a weird anachronism.
Although Irish "home rule" was an issue in the Victorian era of the movie, it was still wholly part of The UK at the time, and so certainly its rulers were still loyal to Britain (violent revolution began in 1916 leading to self-rule of a partitioned area in the 1920's). So Prudent (Henry Hull) was wrong to worry that him selling arms to Britain earlier would result in the Irish authorities persecuting him if he escaped from the Albatross to there.
The British fleet that Robur is bombing consists of ships-of-the-line that date from the late 1700s to the early 1800s, rather than the 1860s.
Robur's ship flies over a battle being waged in the African desert. When he looks through his scope, African scenery appears, but out the front window of the aircraft, the scenery is from what looks like the California mountains.
Robur dangles Strock and Evans from the Albatross dirigible on ropes as a punishment. A storm comes, he clearly sees that, but insists to crew-members that the punishment still continue as he leaves for the bridge to tackle the storm. The storm duly tackled, he then "suddenly" remembers that he has left the two men dangling throughout the storm - but logically he knew that all along by ensuring that the punishment still continue on seeing the storm begin.
Robur may not have been as well educated as he puts on. He named his flying ship the "Albatross", a famous metaphor for misfortune and disaster.
Then again, it is specifically *shooting* an albatross that is said to bring disaster (and indeed for most of the film shooting the Albatross goes badly for anyone who tries it). If the albatross was a particularly unlucky bird in itself you would expect them to be extinct.
At about the 1' 25" mark when Charles Bronson comes out of a door onto the deck to help with the poles he has to duck to avoid being hit on the head with a pole by a crew member.