The Declaration of War states that Grand Fenwick was founded in a year over 50 years distant from what the narrator says at the beginning of the film.
During the Institute for Physics scene, Professor Kokintz addresses Tully as both "Grand Marshall" and "Mr. Constable", but nowhere in the preceding dialogue is Tully introduced as such. Prof. Kokintz couldn't have known his two titles.
After Will Buckley tells the archers to quit shooting at Queen Elizabeth and they stop, the archers are shown shooting arrows at the stern of Queen Elizabeth as she passes.
The narrator tells us that the mock version of Grand Fenwick's wine drove the real wine out of the U.S. market in 1959, but several newspaper pages place the action in February and March of 1958. A BBC news announcer later reports the score of the last game of the 1958 World Series - which he states is the finale of the American version of football.
The newspaper Tully reads is dated in February 1958 but some of the magazines in the rack behind O'Hara when he calls in his report have cover dates of October and November 1958.
When the archers fire on RMS Ivernia as they pass going home, some arrows stick in the "metal" walls of the ship, instead of bouncing off as they should.
In reality the four New York policemen who accompany General Snippet would have been armed, and, no doubt, willing to defend themselves. The police officers weapons would have been holstered while sitting in the jeep and they were immediately surrounded by armed men when the jeep stopped. They would not have had time to draw their weapons and surrender was the logical move.
After Grand Fenwick's army sets sail for home, the headline in one American newspaper (the San Francisco Review) references war mobilisation. American newspapers would spell it mobilization.
The scene when Tully and his men return to Grand Fenwick was obviously shot in segments and pieced together. In the shots of Count Mountjoy and Bentner, one can clearly see their breath (condensation) as they are speaking, but not in the shots focusing on Tully or the Duchess, indicating that those scenes were shot at a time when the weather was colder.
The stormy crossing of the Paladin transporting Grand Fenwick's invasion force to the US was achieved by simply tilting the camera, as exposed by the way the sky moves at exactly the same angle as the deck.
During the montage showing the "empty" Manhattan, there is a driver visible in one of the "abandoned" cars.
Prime Minister Count Rupert of Mountjoy's nose is of a different color than the rest of his face, obviously a fake.
When the band is playing outside Parliament, two band members arrive late and squeeze their way in. Later when preparing to greet the triumphant American army, this shot is used a second time.
General Snippet speaks with Grand Duchess Gloriana XII in the Museum of Ancient Tortures. As Grand Duchess Gloriana XII approaches the General (both seen in profile (her left, his right)) the general's chest is illuminated from the front. The Duchess casts a shadow upon the belly of the general.
However, in the next shot (general viewed from the front) the general's head casts a shadow upon his chest as he is illuminated from above and behind.
General Snippet (MacDonald Parke) and the other US Army officers wear the WWII-era olive drab uniform that was replaced by the green Class A uniform in 1956 (which has only just recently been phased out)
Whilst Tully crossed the Atlantic to New York, We see a newspaper with the day/date Thursday February 11 1958. In 1958, the 11th fell on a Tuesday.
When the General is left alone with the bomb in the speeding car, a rope is clearly visible trailing behind the car as it begins the descent.
The narrator says at the beginning that Grand Fenwick, sized at 15¾ square miles, is the smallest country in the world. Monaco and the Vatican are much smaller, so small, in fact, that even put together they are still much smaller than Grand Fenwick. Monaco itself is approximately 1 square mile. Even smaller is the Vatican, whose area is measured in mere acreage.
Helen Kokintz explains that this bomb is so powerful that "My father uses an H-bomb just to trigger this one." Since there is no H-bomb present it would pose no danger, yet throughout the film everyone is deathly afraid of it.
When the liner Ivernia encounters the ship carrying the Grand Fenwick troops returning from New York, the ship's officer calls "ship off the port bow" and points right (starboard). In the next shot, the troop ship is shown off the liner's starboard bow.
When playing "Diplomacy", one player moves his piece clockwise, the other moves his piece counterclockwise.