Defense Secretary Chuck Hagel speaks during a briefing at the Pentagon on Oct. 30, 2014.

WASHINGTONv - Defense Secretary Chuck Hagel has concluded that problems in the nation's nuclear forces are rooted in a lack of investment, inattention by high-level leaders and sagging morale, and is ordering top-to-bottom changes, vowing to invest billions of dollars to fix the management of the world's most deadly weapons, two senior defense officials told The Associated Press on Thursday.

Hagel ordered two lengthy reviews of the nuclear force after a series of stories by the AP revealed numerous problems in management, morale, security and safety, leading to several firings, demotions and other disciplinary actions against a range of Air Force personnel from generals to airmen.

Hagel's moves, while not dramatic, are designed to get at the core of the problem, the officials said.

The senior defense officials discussed the reviews and Hagel's response to them on condition of anonymity because they were not authorized to be cited by name.

Hagel was expected to announce his decisions at a morning news conference Friday and then fly to Minot Air Force Base in North Dakota, home of a Minuteman 3 missile unit whose recent setbacks are emblematic of the trouble dogging the broader force.

The Air Force has been hit hardest by the problems, particularly its Minuteman 3 intercontinental ballistic missile force based in North Dakota, Montana and Wyoming. The AP documented numerous missteps over the past two years, including misbehavior by ICBM force leaders, lapses in training, violations of security rules and exam cheating.

The Navy, which operates nuclear-armed submarines, had its own exam-cheating scandal this year and has suffered from a shortage of personnel.

Hagel's reviews concluded that the structure of U.S. nuclear forces is so incoherent that it cannot be properly managed in its current form, and that this problem explains why top-level officials often are unaware of trouble below them.

The reviews also found that a combination of problems amount to fundamental flaws, rather than random or period slip-ups that can easily be fixed, the defense officials said. They said the nuclear forces are currently meeting the demands of the mission but are finding it increasingly hard to cope.

When he ordered the two reviews in February, shortly after the Air Force announced it was investigating an exam-cheating ring at one ICBM base and a related drug investigation implicating missile crew members, Hagel was said to be flabbergasted that such misbehavior could be infecting the force.

"He said, 'What is going on here?'" one of the senior defense officials recalled.

Among his more significant moves, Hagel authorized the Air Force to put a four-star general in charge of its nuclear forces, the two senior defense officials said.

The top Air Force nuclear commander currently is a three-star. Lt. Gen. Stephen Wilson is responsible not only for the 450 Minuteman ICBMs but also the nuclear bomber force. Hagel has concluded that a four-star would be able to exert more influence within the Air Force, the defense officials said.

Hagel also OK'd a proposal to upgrade the top nuclear force official at Air Force headquarters in the Pentagon from a two-star general to a three-star, the officials said.

He concluded that despite tight Pentagon budgets, billions of dollars more will be needed over the next five years to upgrade equipment. That will include a proposal to replace the Vietnam-era UH-1 Huey helicopter fleet that is part of the security forces at ICBM bases. The Air Force declared them out of date years ago but put available resources into other priorities.

The defense officials said Hagel would propose an amount between $1 billion and $10 billion in additional investment. An exact amount had not yet been determined.

Hans Kristensen, a nuclear expert with the Federation of American Scientists, said Thursday that while he had not seen the Hagel reviews or heard what actions Hagel was ordering, he was skeptical that it would make much difference.

"Throwing money after problems may fix some technical issues but it is unlikely to resolve the dissolution that must come from sitting in a silo hole in the Midwest with missiles on high alert to respond to a nuclear attack that is unlikely to ever come," Kristensen said.

A cascade of embarrassments befell the Air Force over the past two years, beginning with an AP story in May 2013 revealing one missile officer's lament of "rot" inside the force. Another AP story in November disclosed that an independent assessment for the Air Force found signs of "burnout" and elevated levels of personal misconduct among missile launch crews and missile security forces.

The AP also disclosed last year that four ICBM launch officers were disciplined for violating security rules by opening the blast door to their underground command post while one crew member was asleep.

Just last week the AP disclosed that the Air Force fired two nuclear commanders and disciplined a third, providing evidence that leadership lapses are continuing even as top Air Force officials attempt to bring stability to the ICBM force.

The most senior officer to be relieved Nov. 3 was Col. Carl Jones, vice commander of the 90th Missile Wing at F.E. Warren Air Force base in Wyoming. He had been investigated for inappropriate behavior, including alleged cruelty toward a subordinate.