The U.S. Navy on Sunday tested an unarmed Trident II missile from the USS Maine for the second time in a week. The tests was carried out from an Ohio-class ballistic missile submarine that carries nuclear warheads.

The US Navy conducted its tests on the Western Test Range off the coast of San Diego.

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

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.