A look at findings from AP reporting on troubles in the country's nuclear force

A string of nuclear missteps, many uncovered by The Associated Press, have beset the nation's nuclear force in the last year:

__ Defense Secretary Chuck Hagel orders on Thursday an independent review of the nuclear force and summons the most senior Pentagon leaders to discuss its serious missteps, leadership lapses and personnel problems.

— On Jan. 16, the Air Force said at least 34 nuclear missile launch officers have been implicated in a cheating scandal and have been stripped of their certification in what the Air Force believes is the largest such breach of integrity in the nuclear force. The cheating involves the monthly test on their knowledge of how to operate the missiles.

— As part of the Jan. 16 announcement of the alleged cheating, the Air Force said three ICBM launch officers — two at Malmstrom Air Force Base in Montana and one at F.E. Warren Air Force Base in Wyoming — were among 11 officers at six bases implicated in an illegal-narcotics investigation.

— In April, 17 missile crew members in the 91st Missile Wing at Minot, N.D., were deemed temporarily unfit for duty and given weeks of remedial training. The wing's deputy commander of operations complained of "rot" in the force. Later, the officer in charge of the 91st's missile crew training and proficiency was relieved of duty.

— In August, the 341st Missile Wing at Malmstrom failed a safety and security inspection. Nine days later the officer in charge of security forces there was relieved of duty. In October the unit passed a do-over test.

— On Oct. 11, the Air Force fired Maj. Gen. Michael Carey, commander of the 20th Air Force, which is responsible for the entire Minuteman 3 missile force, amid an investigation of an alcohol-related complaint. This happened two days after a Navy admiral who was second-in-command at U.S. Strategic Command, the military's main nuclear war-fighting command, was relieved of duty amid a gambling-related investigation.

— The AP reported that twice last year the Air Force punished officers involved in separate incidents of opening the blast door of their launch control center while one of the two launch officers was asleep, in violation of Air Force rules.

— In November, the Air Force chief of staff, Gen. Mark Welsh, disclosed that as a result of the Carey firing, the Air Force would take a closer look at the background of candidates for general officer-level nuclear command jobs.

— Also in November, the AP reported that key members of the Air Force's nuclear missile force are feeling "burnout" from what they see as exhausting, unrewarding and stressful work. The finding, in an unpublished RAND Corp. study provided to the AP in draft form, also cited heightened levels of misconduct such as spousal abuse and said court-martial rates in the nuclear missile force in 2011 and 2012 were more than twice as high as in the overall Air Force. The courts martial rate in 2013 declined but was still higher than the overall Air Force.