Complex sentence: After a time, the "Tigershark" finally discovers the cause of the disasters: a saucer-shaped underwater craft with a strange light coming from an eye-shaped window located at the top and in the center of the saucer's upper dome.
Split into simpler sentences: After a time, the submariners do finally find the cause of the disasters: a saucer-shaped underwater craft with a strange light coming out of an eye-shaped window. The window is located at the top and in the center of the ship's upper dome.