Secretary of Defense Ashton Carter has admitted that the US military is not “agile” enough and needs a simplified chain of command.

“In an increasingly complex security environment, and with a decision chain that cuts across the combatant commands only at the level of the secretary of defense, we are not postured to be as agile as we could be,” Carter said at the Center for Strategic and International Studies (CSIS) in Washington on Tuesday.

The Pentagon chief said the “top-heavy” command structure of the US military needs a review and he plans to reduce the number of four-star positions currently in service.

“In the coming weeks the Defense Department will look to simplify and improve command and control where the number of four-star positions have made headquarters either top-heavy or less efficient than they could be,” he explained.

The Pentagon chief added that he plans to keep the chairman of the Joint Chiefs of Staff, currently Marine General Joseph Dunford, out of the wartime chain of command, with the president at top, followed by the defense secretary and field commanders.

Carter, however, rejected the idea of changing the current lineup of Combatant Commands such as Central Command, European Command and Pacific Command which are in charge of planning the wars and fighting them.

Shrinking the top military brass is one of the main ideas for updating the Defense Department's command structure established under the 1986 Goldwater-Nichols Act.

The need for a change has also been echoed by General Dunford, who called for a new military staff that can coordinate military responses across various regions.

Dunford told a Washington defense forum in December last year that America’s current war planning and command and control structure are “not really optimized.”

The Senate Armed Services Committee and its Republican chairman, Senator John McCain, are in the process of rewriting the Goldwater-Nichols Act.