A retired general chosen to explore flaws in U.S. nuclear forces signed off one year ago on a study describing the nuclear Air Force as “thoroughly professional, disciplined” and performing effectively — an assessment service leaders interpreted as an encouraging thumbs-up.

The overall judgment conveyed in the April 2013 report by a Pentagon advisory group headed by retired Gen. Larry Welch, a former Air Force chief of staff, appears to contradict the picture that has emerged since then of a nuclear missile corps suffering from breakdowns in discipline, morale, training and leadership.

That same month last year, for example, an Air Force officer wrote that the nuclear missile unit at Minot Air Force Base, N.D., was suffering from “rot,” including lax attitudes and a poor performance by launch officers on a March 2013 inspection.

It’s unclear whether the Air Force took an overly rosy view of the Welch assessment, which was not uniformly positive, or whether his inquiry missed signs of the kinds of trouble documented in recent months.

Whichever the case, Welch is again at the forefront of an effort — this time at Defense Secretary Chuck Hagel’s personal direction — to dig for root causes of problems that Hagel says threaten to undermine public trust in the nation’s nuclear arsenal.

The most recent such problem is an exam-cheating scandal at a nuclear missile base that prompted the Air Force to remove nine midlevel commanders and accept the resignation of the base’s top commander. Dozens of officers implicated in the cheating face disciplinary action, and some might be kicked out.

Welch began the new Hagel-directed review in early March, teaming with retired Navy Adm. John C. Harvey, who was not involved in the earlier reviews but has extensive nuclear experience.

Much rides on what they find, not least because Hagel and the White House want to remove any doubt about the safety and security of the U.S. arsenal and the men and women entrusted with it.

Hagel’s written instruction to Welch and Harvey in February said they should examine the nuclear mission in both the Air Force and the Navy, focusing on “personnel, training, testing, command oversight, mission performance and investment” and recommend ways to address any deficiencies they identify.

A fighter pilot by training and a former top nuclear commander, Welch also is known for integrity and honesty. Hagel “believes there is no one better suited to examine these issues than Gen. Welch,” Hagel’s press secretary, Navy Rear Adm. John Kirby, said Friday. “Like his partner Adm. Harvey, he’s tough and pragmatic. And he flat-out knows his stuff.”

Welch led the initial outside review of arguably the most startling nuclear failure of recent years, the unauthorized movement in August 2007 of six nuclear-armed cruise missiles from an air base in North Dakota to Louisiana. Welch led that inquiry as chairman of a special task force of the Defense Science Board, which is a group of outside experts who advise the secretary of defense on a wide range of technical issues. The panel’s report was published in February 2008.

The same task force, again under Welch’s direction, published follow-up assessments in April 2011 and April 2013. Each of those examined both sides of the nuclear Air Force — strategic bombers as well as the international ballistic missile, or ICBM, forces whose problems have gained wide attention over the past year.

The April 2011 study cited morale issues among missile crews.

“They perceive a lack of knowledge of and respect for their mission from within the larger Air Force,” it said.

The April 2013 report ticked off numerous significant improvements.

It found that senior leaders were paying more attention, with more clarity of responsibility for the nuclear mission than in the years leading up to the 2007 mishap. The system of inspections and the support for nuclear personnel, logistics and facilities had improved.

Yet at that point the first signs of new trouble had begun to emerge, including the mass suspension of 19 launch officers at Minot in April 2013, followed by a failed inspection in August at another nuclear missile base in Montana.

Welch’s report also cited “enduring issues that require more responsive attention.” And he said the Air Force needed to prove that the nuclear mission is the No. 1 priority it claims it to be. He also found that ground water intrusion in nuclear missile silos and the underground launch control posts to which they are connected had done major damage, including collapsing electrical conduits.

The bottom-line conclusion, however, was this:

“The nuclear force is professional, disciplined, committed and attentive to the special demands of the mission.”