You are most likely talking about the radar, which scans and alerts the people on the submarine of other submarines, missiles, etc. nearby.
As you know, water evaporates in heat, and tropical places are usually very hot! Tropical implies "ocean" so, when an ocean evaporates it leaves a sandy ocean floor, which is a desert, but there are lake sized "puddles" of salt water left over, which is why there is a big salt water lake in the middle of Utah.
Answer:
They journey took me _some_ hours