Factual error: When Ulysses opens his mouth while speaking, modern dental fillings are in his teeth.
Factual error: The Vikings in this episode are fighting while wearing horned helmets. Contrary to popular belief, Vikings never wore horned helmets in battle. Some theories state the horned helmets were worn during special ceremonies, but never in battle or daily life.
Visitors From Beyond the Stars - S1-E18
Factual error: Modern power cables are seen near Crawford's homestead, complete with aircraft warning flags draped over them. These cannot be mistaken for 19th century telegraph wires.
The Revenge of Robin Hood - S1-E16
Factual error: Little John orders the archers to "Fire" - the correct command for archers would have been either "shoot" or "loose."
Factual error: Major Hoffman asks the brainwashed Doug what unit he is with. Doug answers, "74th Panzer Division." Neither the German Army nor the SS had a 74th Panzer Division.
Factual error: While firing their muskets at the guards as they rescue the Dauphin, Tony and Doug each quickly discharge their weapons twice without reloading. Muskets are one-shot weapons that required immediate reloading after firing.
Visitors From Beyond the Stars - S1-E18
Factual error: The aliens show Doug and Tony the planet they plan to invade - Earth, of course. But the special effects department forgot to give poor old Earth any clouds. (There are clouds over more than 70% of our planet at any given time.) When they go down to the surface, though, there are plenty of clouds in the sky. (00:05:20)
Factual error: Wogan the Viking probably shouldn't laugh quite so enthusiastically. When he does, several of his very 20th Century gold fillings are visible. (00:09:30)
Factual error: The Gestapo major's office has a picture of Rudolf Hess hanging on the wall. Not likely, as Hess parachuted into Scotland in 1941 and was considered a traitor to the Third Reich.
Factual error: The battle scenes show the Greek and Trojan cavalry troopers equipped with stirrups on their saddles. The stirrup would not be used until nearly 1,400 years later.
Factual error: Raul Nimon uses a silencer-equipped revolver during his attack in the tunnel control room. In reality, a silencer on a revolver is useless, as the exploding gases from the bullet discharge (the gun blast) would exit from the space between the cylinder and gun barrel.
Factual error: One of the Spanish soldiers lights a torch with what appears to be a hand-held lighter. Early lighters were converted flintlock pistols (not yet invented during the time of this episode) and the earliest hand-held lighter would not be invented until three hundred years after this episode's timeline.
Factual error: Right at the start of the episode there is a sign visible on the side of a building that shows the German word "Warenhaus." This is a wrong translation of the English word "warehouse." The correct German word should be "Lagerhaus."
Factual error: Doug and Tony time travel to one million years B.C., where they encounter dinosaurs. Not likely. All the dinosaurs were rendered extinct several million years earlier by an asteroid strike. There weren't any left by 1-million BC. (00:29:45)
Factual error: This is one of two episodes in the series where a WW2-era German MP38/40 submachine gun was used by American forces (Master Sergeant Jiggs, in this episode) rather than an American weapon such as a Thompson submachine gun.
Factual error: When Doug and Tony recount the causes of the Trojan War, they mention three Roman goddesses - Venus, Juno, and Minerva - instead of using their Greek names - Aphrodite, Hera, and Athena.
