The Pentagon’s outgoing personnel chief on Monday offered a vigorous defense of his controversial tenure Monday, saying his effort to reform how the way the military manages its people has fundamentally changed the Defense Department’s culture.

Brad Carson, who stepped down Friday from his post as the Defense Department’s undersecretary for personnel and readiness, dismissed critics who said the "force of the future" personnel reform effort fizzled out amid political resistance from the military's senior military leadership top brass.

"I think these ideas are going to prevail," Carson said Monday at the Center for Strategic and International Studies, a think tank in Washington.

"The entire building is saying we have to think differently now," he said, referring to the Pentagon. "That is a remarkable achievement. ... I think we'll be remembered for decades for pushing this."

"It has been the most historic year for personnel reform in the history of the Defense Department," he said

Carson held the Pentagon's top personnel job for one year. Initially he vowed to seek "revolutionary change" and his early proposals called for changing the military's up-or-out promotion system, which forces officers to leave the service if they fail to be promoted within rigid timelines.

The military personnel system should emphasizes talent rather than seniority, he said. And he suggested giving pay raises for troops with high-demand skills and creating new ways for mid-career civilians to join the military without having to start at the bottom of the rank structure.

Yet many of those ideas have not yet emerged as formal Defense Department policies or proposals. Instead, Defense Secretary Ash Carter has publicly announced more incremental changes, like expanding the force-wide maternity leave benefit, expanding pilot programs for troops who want to spend time working in the private sector and a new means to analyze personnel data to improve how the services assign troops to specific jobs and retain them for long careers.

Carson said some of those changes remain in the works. "I think you're going to see in the next few weeks a lot of movement," he said.

He avoided any criticism of his former boss. "Dr. Carter has been a terrific supporter," Carson said of the secretary.

Carson is leaving after a disastrous confirmation hearing on Capitol Hill in February. Senators accused him of presuming confirmation and violating a once rarely enforced law that bars new appointees from serving in their high-level positions while awaiting the Senate's formal approval.

Underlying that was the controversy surrounding Carson's personnel reform effort — which Sen. John McCain, R-Ariz, called "an outrageous waste of official time and resources." Carson said he decided to step down because he'd wrapped up his recommendations to the secretary and "the work was done."

Carson will be replaced by Peter Levine, an longtime staffer for the Senate Armed Services Committee who also served as Carter's senior adviser on how to streamline the Defense Department's overhead functions.

Carson ter acknowledged that his effort to rewrite personnel rules that have been in place for decades did spark fierce debate. "It should be controversial. This work is extraordinarily important," he said. But he pushed back on the suggestion that Pentagon politics turned against him.  

"In no way do I think of the politics of this in a bad way. …There was never a situation when people said … I will fight you," Carson said.

Carson described himself as a "policy entrepreneur," saying he did not develop new ideas but instead assembled years of research from top personnel experts and sought ways adapt them for the day-to-day management of the Defense Department.

Changing the military's up-or-out rules, as codified in a 1986 federal law known as the Defense Officer Personnel Management Act, was among the most controversial elements of Carson's reform effort. Changing that would require approval from Congress.

He appeared to acknowledge that the biggest resistance to changing the up-or-out promotion system came from the Army and Marine Corps. "People in the combat arms, they think up-or-out works better for them," he said.

But he also said that without changing those rules, other reform efforts would fall flat. That’s because many officers will fear that taking time to get a graduate degree, work in the private sector or pursue an otherwise non-traditional career path will put their career in peril.

"We can have sabbaticals. But if they don't get promoted when they come back in, they won't take them. They will realize these are career killers," he said.

Carson said he's known many talented junior officers who left the military after just a few years due to frustrations about the way the institution is run. "There was an astonishing number who said 'The bureaucracy got me down.'"

"What leads a person to separate from the Army at the O-3 level?" he asked rhetorically, referring to the point in junior officers' careers when many chose to leave.

"We can't really answer that question," Carson said.

"The best people in the military — are they staying? Or are they leaving? The answer is that no services can answer that question. … That is, to me, unacceptable."