A Trident II D5 missile is launched from a submarine in 2014. Navy photo

The U.S. Navy on Sunday conducted its second test in a week of an unarmed Trident II missile from the USS Maine, an Ohio-class ballistic missile submarine that carries nuclear warheads.

This 7 a.m. test — on the Western Test Range off the coast of San Diego — follows the Maine’s “Demonstration and Shakedown Operation” conducted Wednesday, also on the Western Test Range.

Sunday’s scheduled test “validated performance expectations” of the Trident II Strategic Weapon System, and gathered additional data on the SWS’ reliability, accuracy and performance factors, the Navy said.

Sunday’s launch marked 178 successful missile launches of the Trident II strategic weapon system, the Navy said.

Test launches are conducted on a recurring basis to evaluate and ensure the continued reliability and accuracy of the strategic weapon system.

“Strategic Systems Programs is the Navy command that provides cradle-to-grave lifecycle support for the Navy’s Submarine Launched Ballistic Missile Trident II (D5LE) strategic weapon system,” the Navy said.

SLBMs are the sea-based leg of the nation’s strategic nuclear deterrent triad that also includes the U.S. Air Force’s intercontinental ballistic missiles and nuclear-capable bombers.

The sea-based leg makes up about 70 percent of the U.S.’s deployed strategic nuclear deterrent Triad.

Last September, four unarmed Trident IIs were launched off the coast in similar tests.

Those tests were part of a program to extend the strategic weapons system’s lifespan into the 2040s.

“Our nation’s sea-based deterrent has been a critical component of our national security since the 1960s, and this week’s launches continue to demonstrate the credibility and reliability of our life-extended missiles,” Vice Adm. Johnny R. Wolfe, director of the the command responsible for the Navy’s strategic weapons, said last year.

The 45-foot-long missiles have a range of 4,000 nautical miles and carry either eight or 14 independently targetable thermonuclear warheads.

They are deployed on 14 Ohio-class submarines, each of which had 24 of the weapons. The submarines are nicknamed “boomers” because of their missiles’ destructive power.