Lieutenant Juan "Gator" Mejia is a navigator aboard the USS Nathan James. He is responsible for the coordinates and conditions that affect the ship's direction and movement. The name "Gator" is shorthand for the title of Navigator.
While Gator is an expert on the computerized navigation equipment, he has also proven that he can navigate without it if necessary. He got the NJ through a narrow coral reef when the ship was escaping the Russians after the Russians mined the area around the ship to keep it from escaping. The NJ was on radio and radar silence, so Gator had to use pen and paper to plot their course.
Gator is also very aware of the various land masses surrounding the ship at any time. He identified the island where the ship could stop and make crucial repairs to the engine. It took six days and the crew ran out of water, but they made it.