The Tunnel

One of the plot elements that crops up in the movie is a volcanic area that the tunnelers run into about halfway across the Atlantic. This makes sense, as the Mid-Atlantic Ridge is a very active area. The neat part in relation to the movie is that while the existence of a "Ridge" on the seafloor was known at the time, it was not known that it was so active. It wasn't until the Heezen/Ewing/Tharp mapping of the ocean floor in the 1950s that people discovered that Seismic activity and "Seafloor Spreading" due to magma seepage were going on. That was about 20 years after the makers of the film surmised Magma pockets near the Mid-Atlantic.

Although the story takes place over a period of about twenty years, none of the principal players shows any sign of aging, despite all the ordeals encountered.

At the end of the opening credits, a card comes up with "Gaumont-British Picture Corpn. Ltd. were fortunate in securing the services of Mr. George Arliss and Mr. Walter Huston for the parts of Prime Minister of Great Britain and President of the United States."

Edited from Il tunnel (1933)