The Defense Department and the military services have convened several major investigations into the nuclear mission since the Air Force’s first raft of nuclear-weapons scandals in 2007 and the Navy’s recent discovery of answer-sharing on tests. And distinguished panels of current or former leaders have looked into the incidents and submitted their findings in hundreds of pages that the brass promised to take on board.

The problem is, they didn’t seem to take, and officials aren’t sure why.

“I don’t think there is one simple answer to the issue of ethics, values, a lapse in some of those areas that we do know about,” Defense Secretary Chuck Hagel told reporters the other day at the Pentagon. “That’s why we’re taking a hard look at this.”

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So far, no one has been fired in the Navy or Air Force scandals. Hagel said the Pentagon would hold people accountable if necessary, but first he wants a better sense of the ethical and moral health of today’s force.

“We need to find out, is there a deep, wide problem?” he said. “If there is, then what’s the scope of that problem? How did this occur? Was it a constant focus of 12 years on two long land wars, taking our emphasis off some of these other areas? I don’t know. We intend to find out.”

Hagel said he plans to appoint a general officer as a top ethical adviser for the Pentagon. He has also appointed another distinguished panel to look at the troops and units of the nuclear force, as well as an independent review helmed by a former Air Force chief of staff and a retired top Navy admiral. And the defense secretary expects an “action plan” this spring to serve as a blueprint for his next moves.

Former Defense Secretary James Schlesinger’s blue-ribbon panel also made recommendations in its report in 2008. So did former Adm. Kirkland Donald, in his mostly classified report. In 2011, the Navy’s inspector general opened, and then dismissed, an investigation into answer-sharing aboard the fast attack submarine USS Memphis — even though its captain and several crew members lost their jobs.

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So when Chief of Naval Operations Adm. Jonathan Greenert was asked last week why he thought a cadre of 30 senior nuclear power instructors in Charleston, S.C., might risk their jobs by potentially cheating on their exam, he shook his head.

“If I knew that answer, I would be doing all kind of things within the Navy,” Greenert said. He vowed that this investigation would go as deep or wide as necessary to keep it from happening again. “We will be very introspective on this.”

Introspection has already wrought some changes to the force. Schlesinger’s report found that the Air Force had essentially forgotten its nuclear units after the end of the Cold War, leaving them as orphans inside the bureaucracy and causing its latest round of problems. That’s why the Air Force mistakenly shipped ballistic-missile nose cones to Taiwan, instead of helicopter batteries, and loaded live nuclear weapons aboard a bomber that flew them across the U.S. without anyone realizing.

So the Air Force consolidated its units under a new Global Strike Command and cracked the whip over nuclear-readiness inspections — but that didn’t prevent the widespread transgressions that came to light last month. The Air Force says at least 13 airmen, three of whom belong to Global Strike, and its investigation into the drugs is what led to the discovery that some 92 airmen are involved with an alleged cheating ring.

The Navy’s nuclear cheating situation in Charleston follows problems with the forging of records — “gundecking” or “radioing,” in sailor-speak — aboard the fast attack sub USS Hampton in 2007 and test cheating aboard at least two aircraft carriers and the Memphis. Navy inspectors looking into the Memphis case decided there wasn’t enough evidence about widespread cheating in the nuclear force to justify a larger-scale investigation, but skeptics said at the time that the Navy just didn’t want to look for something it didn’t want to find.

According to documents described at the time by The Associated Press, the anonymous sailor who complained about the Memphis’s cheating did so because he thought it was unfair that he’d been singled out for punishment when it was so commonplace among the crew. He argued that his reprimand was comparable to being caught driving at 60 miles per hour in a 55 zone and losing his license for life, while all the other drivers kept on speeding.

The head of the Navy’s submarine force, then-Vice Adm. John Richardson, cited the Memphis case at the time as an example of why the fleet depends on integrity. Since then, Richardson has been promoted to full admiral and become boss of the entire Navy nuclear-power program — and he acknowledged that with the Charleston discovery it may now be time to survey the whole nuclear fleet.

“We’re looking across the entire program,” he said. “So we’ll start there. That’s where our concern is most acute right now. We’ll make sure that we have taken a look at the entire program.”

If there’s a silver lining, officials say, it’s that the people involved with the Navy and Air Force cases represent just a small fraction of their total population — Richardson said there are about 16,000 people in the total Navy nuclear power program, compared to the 30 instructors who have been suspended in Charleston.

Not so with another story that has popped into the headlines in an unhappy coincidence for the Pentagon. It’s a National Guard recruiting scandal in which soldiers, retirees and civilians are said to have abused a program that paid incentives for bringing people into the force. Commanders launched the program in 2005, at a time in the Iraq War when the Army was eager to bring in as many people as possible.

The scale of the problem could be many orders of magnitude greater than the Air Force and Navy scandals. The Army’s Criminal Investigation Division is reviewing the cases of more than 106,000 people who were paid under the bonus program, a process it said could go on for two more years. Officials told a Senate hearing led by Missouri Democrat Claire McCaskill that the Army has so far prosecuted 104 people, and that soldiers of all ranks, including colonels and generals, are under investigation.

“The complete lack of controls and safeguards on this program created a culture of permissibility where it didn’t take much for thousands of people to figure out that fraud would be easy,” McCaskill said. “One of my biggest concerns is holding people accountable, and it breaks my heart to discover that there are criminals who have dishonored the uniform that we are all so proud of.”