While the size of the Defense Department’s workforce has climbed significantly in the post-9/11 era, a new report has found the Pentagon has no system in place to justify the number of people it employs.

Defense headquarters and its military components -- the Army, Navy, Marine Corps and Air Force -- all fail to systematically determine their personnel requirements, the Government Accountability Office found. Staffing levels at the Office of the Secretary of Defense and the military secretariats have dropped off in recent years, but without greater oversight, the offices cannot ensure the size of their workforces matches their workloads.

“Without a systematic determination of personnel requirements and periodic reassessment of them, DoD will not be well positioned to proactively identify efficiencies and limit personnel growth within these headquarters organizations,” GAO wrote.

In 2013, outgoing Defense Secretary Chuck Hagel called on all Defense headquarters offices -- including his own -- to reduce their budgets by 20 percent through fiscal 2019. Those plans are already under way, but GAO found the Pentagon has yet to spell out exactly how it will achieve the required savings.

In the 1980s and 1990s, Congress imposed statutory limits on the number of employees at Defense headquarters offices. Since 2002, however, those limits have been waived. If the former limits were still in place for fiscal 2013, the Navy would have exceeded them by 74 percent, GAO noted, offering that as an example of potential overgrowth.

OSD, the Navy and the Marine Corps have all taken steps to better track their required personnel levels, though they have not finalized any processes to implement the improved oversight. The Army has not created any such system, GAO found.

The watchdog advised the Defense Department to devise a systematic way to assess the mission, function and tasks of each component and the minimum number of employees needed to complete them. The Pentagon should also ensure the results are reviewed regularly. GAO also called on Congress to use Defense’s review to create new statutory limits on personnel.

Some lawmakers have their own ideas for capping the number of employees at Defense; earlier this week, Republican House members introduced a bill to slash the number of civilians at the agency by 115,000.