The real U-33 of World War One served in the Mediterranean and survived the war.
Amicus cast Stuart Whitman in the lead. AIP refused to finance the film if Whitman starred, so he was fired.
This film was featured and riffed in the Netflix series Mystery Science Theater 3000: The Return: The Land Time Forgot (2017).
Michael Palin found a gun from this production in a skip in the studio where this was shot. He kept it.
Doug McClure replaced Stuart Whitman.
German actor Anton Diffring dubbed John McEnery's voice as Captain Von Schoenvorts, allegedly because the producers felt McEnery had used a silly voice for the part.
Announced at the time as being the most expensive production Amicus had undertaken up to that point. Though the film was a co-production.
In the German Version, the Captain is called von Schönfeldt.
According to the movie and the original book by Edgar Rice Burroughs, (fictional) Italian explorer Caproni, who followed Captain James Cook, discovered an island near Antarctica and named it Caprona in 1721. However, this would have been impossible in real life as Cook was not born until 1728.
Bradley was offered to Patrick Mower.
An ichthyostega, a very large prehistoric amphibian that looks like a cross between a frog and a toothless crocodile, is clearly visible on the lagoon's shore.
The Native clans are: Bo-Lu, Sto-Lu, and Ga-Lu.
The first dinosaur in the movie is a Plesiosaur.
Ahm knows what oil is.
Michael Moorcock has said his original script was faithful to the book. But the last 20 minutes were changed by the producers to include the volcano and caveman attacks on the Tyler's men and destruction of the submarine.
Originally Bradley was to get out of the Sub before it was destroyed.
Bowen Tyler and Lisa Clayton are the only survivors.