Danger Beneath the Sea is a 2001 American made-for-television action film directed by Jon Cassar, and starring Casper Van Dien.
Detecting radioactivity in the air and believing the world to be at nuclear war, the executive officer takes command of the ship from the captain and prepares to fire the submarine's nuclear missiles at targets in Russia.
Some members of the crew do not believe they are at war and help the captain take back control of the ship.
In the end, the captain is successful in regaining control of the vessel and preventing the missile launch.
After outmaneuvering the other submarine, the captain surfaces in a Russian harbor and uses a mobile phone (gained from a crewman who brought it on board during a stop-over in Tokyo) to contact an admiral and inform them that the situation is now under control.