I suppose modern computer generated technology has made films like these look dated but this film does have charm despite the deficiencies of a modest budget, eg the same model is used in the sinking of the merchantman at the beginning and the German supply ship. It tells the story of the crew of a sunken British merchant vessel and the crew of a German submarine who find a lost world of dinosaurs and cavemen in the South Atlantic. Ultimately the special effects are a bit ropey but the film is fun. What I like most is the way that the film has the courage to end on a grim note with the hero and heroine lost with the sinking of the submarine which conveniently paved the way for a number of sequels.
Starts rather silly and gets more and more silly as it goes on . U-boats did not waste torpedoes on single merchantmen in 1916 - they gave the crew time to get into the boats then sank it with gunfire. Where did all those barrels come from? Why did the U-boat sink at the end? Fantasies to succeed must create their own laws ans stick to them. And the dinosaurs are pathetic.