Definition: In this task, you're given five sentences, numbered 1 through 5. Your job is to generate a title for the story that makes complete sense. The title must be short, with less than three words, use simple language, and include the main topic of the story.
Input: Sentence 1: Frederick looked out from the periscope. Sentence 2: He saw a ship at the surface. Sentence 3: He alerted the captain. Sentence 4: The captain alerted the crew to prepare to go to depth. Sentence 5: The submarine dove under the surface.

Submarine