In this photo from Feb. 14, 2014, a member of the 91st Missile Security Forces Squadron checks the perimeter of a facility near Minot Air Force Base, N.D. The base recently reported a box of grenade rounds and a machine gun missing. (Staff Sgt. Jonathan Snyder/U.S. Air Force)

Dangerous equipment has once again gone missing at the U.S. Air Force base in North Dakota that operates aircraft and intercontinental ballistic missiles that can deliver nuclear warheads.

Days after Minot Air Force Base reported that one of its squadrons protecting intercontinental ballistic missile silos had lost a 42-pound box of explosive grenade rounds while traveling on a gravel road, the same base said a machine gun turned up missing in a routine inventory of the facility’s weapons.

“During a standard weapons inventory at Minot Air Force Base in North Dakota on 16 May, a M-240 7.62 caliber weapon was discovered missing,” the base said in a short statement on Thursday. “The 5th Bomb Wing and 91st Missile Wing immediately began a search of their weapons inventories and opened an investigation with the Air Force Office of Special Investigations.”

The loss or misplacement of dangerous weaponry is typically taken extremely seriously in the U.S. military, almost always prompting investigations and sometimes follow-on disciplinary measures.

According to Military.com, the M240 is a general-purpose, gas-operated, open-bolt machine gun that can fire at a maximum rate of 950 rounds per minute at a maximum distance of more than two miles. It’s a common weapon used across the U.S. armed forces.

Minot Air Force Base said the investigation into the missing machine gun remained ongoing and added that it would disclose new information as it becomes available.

Lt. Col. Jamie Humphries, a spokesman at the base, said he couldn’t speculate on whether the incidents were the result of theft or other wrongdoing rather than accidents.

Security forces assigned to strategic Air Force bases such as Minot are armed with weapons including machine guns and grenade launchers to protect the installations that house the nation’s nuclear warheads, missiles and bombers.

In addition to operating intercontinental ballistic missile silos, the North Dakota base is home to the B-52 Stratofortress, the long-range heavy bomber capable of flying at high subsonic speeds and dropping nuclear warheads on enemy targets.