The film, which is a British-American co-production, stars Doug McClure, John McEnery, Keith Barron, Susan Penhaligon, Anthony Ainley and Declan Mulholland.

During World War I, Bowen Tyler and Lisa Clayton are passengers on the ship torpedoed by Captain von Schoenvorts.

Von Schoenvorts has his crew steer toward a safe sea port, but German officer Dietz breaks loose and smashes the sub's radio.

Off course and running out of fuel in the South Atlantic, the U-boat and its crew happen across an uncharted subcontinent called Caprona, a fantastical land of lush vegetation where dinosaurs still roam, co-existing with primitive man.

He abandons Tyler and Clayton in Caprona in an attempt to escape, but the U-boat cannot function in the boiling waters, and the crew is killed as it sinks.

Amicus originally wanted to cast Doug McClure in the lead, but he refused, so they signed Stuart Whitman.

Then Samuel Z. Arkoff of American International Pictures came on board as co-financers, providing the bulk of the budget, but would only make the film if McClure was cast.

Also, we developed the use of a small VistaVision camera to shoot the dinosaur back-ground plates which gave us great quality because the exposed frame is twice the size of a normal 35mm.

[10][11][12] The New York Times described the film is "an initially agreeable picture about the discovery of a mystery realm where various stages of evolution coexist", but "the early virtues of Land collapse once the island is reached and the traffic jam in artificial monsters develops.