Defense Secretary Ash Carter has launched a review of the landmark 1986 Goldwater-Nichols Act that has defined military careers and organizational structure for decades, a Pentagon spokesman said Tuesday.

"The secretary feels (it) is important to take a look at the department and the structure right now within the DoD and to make sure that we're doing things as efficiently as possible," said Peter Cook, Carter's primary spokesman.

"This is something that he's initiated here within the department itself, to take a hard look at … whether or not things could be done differently in the spirit of Goldwater-Nichols and the changes that resulted from that many years ago," Cook said at a news briefing.

The Goldwater-Nichols Act fundamentally transformed the military's traditional chain of command by empowering combatant commanders to report directly to the defense secretary, bypassing their service chiefs.

The law also created a requirement that all general and flag officers must serve in a joint-service position outside their own military service. That rule, drawn up in the wake of the Vietnam War, was intended to minimize parochialism and force senior officers to communicate more effectively across service lines.

Lawmakers on Capitol Hill also also have been scrutinizing the legacy of Goldwater-Nichols in a series of recent hearings.

Critics say the geographical combatant commanders have become bureaucratic machines and that real warfighting is now conducted by task forces — for example, Combined Joint Task Force Operation Inherent Resolve, which oversees the mission in Iraq and Syria.

And critics say the joint-billet requirement has achieved its original goal and should be reformed or removed to help make today's military more flexible.

Under current laws, promotion boards are required to look unfavorably on officers who do not fulfill the joint-billet requirement. But critics say that requirement forces some troops to waste time in joint billets that do not comport with their personal career goals or maximize their technical expertise.

They also say the law is hindering the Pentagon's effort to reduce the size of its headquarters structure, a longstanding goal cited as a necessary budget-cutting measure but encountering stiff bureaucratic resistance.

"They need that headquarters structure to get joint-duty billets for everybody ... there just are not enough (joint) jobs without it," John Hamre, head of the Center for Strategic and International Studies, told the Senate Armed Services Committee at a November hearing.

"We've got to figure out … how do we take pressure out of the system so we're not feeding big headquarter structures that are really doing too much micromanagement?" said Hamre, who helped author the Goldwater-Nichols law three decades ago.

Cook said Carter's review will include input from experts inside and outside the Defense Department and may lead to a slate of recommendations in the next several months.

"He's looking early into next year to have some recommendations to move forward," Cook said. "I know Congress is looking at some of these issues as well, and the secretary welcomes the interest of Congress."

Carter likely will consider both "initiatives that he can carry out here on his own and things that might require some congressional action," Cook said.