Yes, and they found the heat source to be volcanic. And in the process they discovered a long lost forgotten world inhabited by dinosaurs and strange tribes of human-like creatures believed to be proto-liberals.
"The Land That Time Forgot"
"Negotiating an underwater tunnel [beneath the ice] to gain the island's interior, those aboard U-33 are amazed to discover a tropical prehistoric world kept warm by volcanic forces. Here dinosaurs that should be long extinct live and roam, as do a curious race of humanoid savages that appear to exhibit all the various phases of Man's evolutionary development. To survive long enough to repair and replenish the U-boat, wartime enemies must put aside their differences and cooperate with one another. But not everyone is playing from the Kumbaya songbook...
The Land That Time Forgot is a thoroughly old fashioned sci-fi/fantasy adventure of the type they weren't really making anymore even in 1975. A lot of this has to do with the script sticking to Burroughs' Victorian style. (His Caprona tales were first published in 1918; as late as World War II he'd still be cranking out novels in the writing style of the 19th Century.) The film's a throwback to the likes of the original King Kong and potboilers such as Unknown Island (1948) and The Land Unknown (1957), only in color."
http://www.eccentric-cinema.com/cult_movies/land_time_forgot.htm
YouTube trailer: The Land That Time Forgot
http://www.youtube.com/watch?v=beirEaMzV-s