A U.S. Navy submarine has conducted four successful Trident II D ballistic missile test flights over a three-day period.

The submarine, which was unidentified in a U.S. Navy report, was an Ohio-class vessel and part of Submarine Group 9, which operates in the Pacific.

Trident II carries a thermonuclear warhead and is part of the nuclear deterrent triad of the United States.

The Navy said the flights were conducted under a Follow-on Commander's Evaluation Test, which is to evaluate, under operationally representative conditions, the reliability, accuracy, and performance of the missile system for use by Commander, Strategic Command and the Joint Chiefs of Staff.

"Safety of the public was paramount throughout the mission," The Navy said. "The missiles were unarmed and all launches were conducted from the sea, flew over the sea, and landed in the sea. At no time did the missiles fly over land."

The flight tests were completed Thursday.