The air force stripped the three airmen of their nuclear certification following the incident in 2014 and quietly launched an accident investigation

Errors by three airmen troubleshooting a nuclear missile in its launch silo in 2014 triggered a “mishap” that damaged the missile, prompting the Air Force to strip the airmen of their nuclear certification and quietly launch an accident investigation.

In a statement, the Air Force declined to provide details of the incident or a copy of the report produced last November by the Accident Investigation Board, saying the information was classified and too sensitive to be made public.

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Under the Air Force’s own regulations, Accident Investigation Board reports are supposed to be made public. The Air Force did release a brief summary to the Associated Press after it repeatedly sought answers for more than a year. The summary said the full report was classified by General Robin Rand, who took over as commander of Air Force Global Strike Command in July 2015.

The Air Force said the accident caused no injuries and posed no risk to public safety. It said top Pentagon officials were briefed on the results of the investigation in December, as were members of Congress.

The damaged missile was removed from its underground silo, which is designated Juliet-07 and placed among wheat fields and wind turbines about nine miles west of Peetz, Colorado. The silo, one of 10 in a cluster that straddles the Colorado-Nebraska border, is controlled by launch officers of the 320th Missile Squadron and administered by the 90th Missile Wing at F.E. Warren Air Force Base in Wyoming.

The accident follows a period of turmoil inside the nuclear missile corps amid an emerging national debate about the costs and benefits of investing hundreds of billions of dollars to modernize the entire strategic nuclear force at a time when war craft is changing.

The Minuteman 3 is the only land-based intercontinental ballistic missile in the nuclear force. First deployed in 1970, it long ago exceeded its planned service life, and the Air Force is developing plans for a replacement.

The Air Force’s brief summary of the Juliet-07 mishap said the Minuteman 3 missile “became non-operational” during a diagnostic test on the evening of 16 May, 2014. The next morning a “mishap crew” chief, who was not identified, “did not correctly adhere to technical guidance” during troubleshooting efforts, “subsequently damaging the missile.” No further details about the damage or errors were revealed.

The investigation report summary said the actual cause of the accident, established by “clear and convincing evidence,” is classified. It said there were four contributing factors to the accident, of which it identified two. One was the mishap chief’s failure to follow technical guidance. The other was that the mishap chief “lacked the necessary proficiency level” to anticipate the consequences of his actions during the troubleshooting.

In seeming contradiction of that second point, the Air Force said in its separate statement to the AP that the mishap team chief was properly trained for the task he was performing. It said he and two other airmen on his team were immediately stripped of their certification to work with nuclear weapons. They remained decertified for “over a year,” until they were retrained and returned to nuclear duty.

Lt. Col. John Sheets, spokesman for Air Force Global Strike Command, said it is possible that some or all of the three could still face disciplinary action.

To prevent a recurrence of their mistake and the accident it caused, the Air Force said it has “strengthened” technical guidance, modified training curriculum and shared information about the conditions that led to the mishap with other units that operate Minuteman 3 missiles.

Lt. Gen. Jack Weinstein was commander of the ICBM force at the time of the incident. The AP requested an interview with him but the Air Force declined to make him available. Weinstein is now the top staff officer on nuclear matters at Air Force headquarters in the Pentagon.

Facebook Twitter Pinterest The Pentagon. Photograph: STAFF/AFP/Getty Images

At times the Air Force has been slow to acknowledge its nuclear missteps. In 2014 then-Defense Secretary Chuck Hagel expressed concern that personnel failures were squandering public trust in the nuclear force.

The most recent previous Air Force investigation of an accident at an ICBM launch silo was in 2008. That investigation, which was publicly released, found that a fire in a launcher equipment room went undetected for five days. It uncovered the remarkable fact that the Air Force was using duct tape on cables linked to the missile.