Below is video footage filmed at 6pm (PST) on 11/7/15:
“At San Onofre beach in southern California. Started as a fireball coming over the ocean, reflecting off the water and showing heat distortion. Explodes at :28 and spent the next five minutes as a glowing, expanding gas cloud radiating down to the surface. It left a blue cloud in the sky for 10 minutes. No sound during the explosion.”
Authorities claimed it was part of a training exercise designed to ensure the military’s ability to operate in urban environments and to prepare forces for upcoming overseas.
“Mysterious maneuvers over the Pacific are forcing a change in Los Angeles International Airport landings late at night, meaning noise for thousands of people in the flight path. Instead of landing from the east over Inglewood, planes begin flying from the west and over the ocean to keep noise levels down, but due to secret military operations, the airspace over the Pacific is closed to incoming flights for the next week.”
The Trident missile is a submarine-launched ballistic missile (SLBM) equipped with multiple independently targetable reentry vehicles (MIRV). The Fleet Ballistic Missile (FBM) is armed with thermonuclear warheads and is launched from nuclear-powered ballistic missile submarines (SSBNs). Trident missiles are carried by fourteen active US Navy Ohio-class submarines, with US warheads, and four Royal Navy Vanguard-class submarines, with British warheads. The original prime contractor and developer of the missile was Lockheed Martin Space Systems. The missile is named after the mythological trident of Neptune. 
Below, videographer, Spiro, give his explanation: