Release Message:  A U-boat, low on fuel, surfaces in a tropical river teeming with primitive and extinct creatures. Written by Edgar Rice Burroughs.

Description:  A U-boat, low on fuel, surfaces in a tropical river teeming with primitive creatures extinct elsewhere; attacked, it submerges again and travels upstream in search of a safe harbor. It enters a thermal inland sea, essentially a huge crater lake, whose heat sustains CapronaÍs tropical climate.