The primary goal of the tests were "to validate performance expectations of the life-extended Trident II"

A US ballistic missile submarine has tested four life-extended Trident II D5 missiles to validate their performance, the US Navy said in a statement on Friday.

Two tests were conducted by USS Nebraska on Wednesday and Friday respectively off the coast of Southern California, the statement said, adding all tests occurred before sunrise, the Xinhua news agency reported.

The primary goal of the tests were "to validate performance expectations of the life-extended Trident II strategic weapon system," the statement said.

The Trident II strategic weapon system, originally designed with a life span to 2024, recently underwent a life extension that will keep it operational through the late 2040s.

The life-extended missiles will serve for the remaining service life of the US Ohio-class and UK Vanguard-class ballistic missile submarines, and as the initial loadout for the US Columbia-class and UK Dreadnought-class ballistic missile submarines.

The USS Nebraska is an Ohio-class ballistic missile submarine.