In the last several years, the Pentagon has brought more than 165,000 soldiers home from combat. It has shaved the end strength of each service, and it has put needed maintenance and modernization of its warships and aircraft on hold to scrape up the savings to meet sequester cuts.

So why does its back office keep growing?

“It makes no sense,” Mackenzie Eaglen, a resident fellow at the American Enterprise Institute, told the Washington Examiner. In the initial response to the Sept. 11 terrorist attacks, “we grew the force and we grew the civilian support.” So it would make sense that as active duty forces drawdown, so would the staff managing them.

But the overhead hasn’t shrunk. The numbers of authorized staff at the Office of the Secretary of Defense and the Joint Staff have grown by about 30 percent since 2009, from about 3,200 military and civilian personnel manning those offices — at the height of the surge – to about 4,200 today, according to a report released by the Government Accountability Office last week.

Beyond the top offices, almost 750,000 additional Defense Department civilians are on the payroll – up from 702,000 in 2009.

This week, the Pentagon's service chiefs will make an all-to-familiar trek to Capitol Hill, where they will warn lawmakers of the dire effects the sequestration cuts are having on their war-fighting capabilities. But there are savings to be had if the Defense Department had looked harder at the size of its civilian workforce.

The Pentagon has taken steps in the last few years to address its headquarters overhead. Both former Defense Secretary Robert Gates and outgoing Defense Secretary Chuck Hagel started efficiency initiatives to cut the Pentagon’s workforce. But government watchdogs assessing the reforms have noted that the Pentagon doesn’t have the mechanisms in place to be able to save as much as officials want. In the Gates’ effort, the Defense Department significantly miscalculated the savings it would achieve partly because it didn’t have a reliable way to identify which personnel counted as part of its headquarters staff.

In Hagel’s review, known as the Strategic Choices and Management Review, or “SCMR,” he directed the Pentagon to come up with a plan by June 2014 to reduce headquarters budget by 20 percent by 2019, but as the GAO reported, that plan had not been issued as of December.

In that same report, GAO found that the Pentagon doesn’t have a requirements process to determine whether its headquarters personnel levels are appropriate, and it doesn't periodically reassess personnel to see if staffing levels are correct.

“I know I sound like a broken record,” said Eaglen, who among many other defense experts in the area, has spent years trying to get the Pentagon to shrink its bureaucracy. “But this is completely unsustainable.”

From 2013 to 2014, the Defense Department cut its active-duty strength by 72,000 troops. The Army shed the lion’s share, 42,000. The Air Force shed almost 18,000 positions, the Marines, almost 12,000. Only the Navy got by relatively unscathed, losing on 350 spots.

The choice is hard in the military, but it is simpler to cut personnel levels than to change the way the military is paid, at least for now, Eaglen said.

On the civilian side, unless significant personnel cuts are made, the Pentagon will have to keep taking sequestration savings from its procurement and modernization accounts.

The reluctance to significantly reduce civilian levels, Eaglen said, “is a bill that only grows.”