The Pentagon's top personnel chief — the architect of the controversial "Force of the Future" personnel reform initiative — has resigned.

Brad Carson, who served as acting undersecretary of defense for personnel and readiness, will leave his post on April 8, according to defense officials.

At the same time, Carson's senior adviser, Morgan Plummer, a former Army officer and central figure in the personnel reform effort, will also step down, defense officials said.

Carson, a 49-year-old former congressman and Iraq War veteran, was tapped for the job in April 2015 and oversaw implementation of several controversial changes to military personnel policy, including the recent decision to open combat jobs to women with no exemptions.

Carson also became the public face of Defense Secretary Ash Carter's ambitious effort to modernize the military personnel system, which faced stiff opposition from some corners of the Pentagon.

Carson recently completed the year-long effort and passed along to the secretary a slate of final recommendations, which may include a call for major changes to the federal law that defines military officers' career tracks, defense officials said.

The departure also comes after Carson's disastrous confirmation hearing on Capitol Hill in February. Senators accused him of presuming confirmation and violating a once rarely enforced law that bars new appointees from serving in their high-level positions while awaiting the Senate's formal approval.

Combined with controversy surrounding the personnel reform effort — which Sen. John McCain, R-Ariz, called "an outrageous waste of official time and resources" — Carson's chances at confirmation before the end of the Obama administration appeared slim.

Carson notified his staff by email Monday afternoon.

"Given the extraordinary work that we've already achieved to date, low likelihood of confirmation even after recusing myself, and reduced time left in the administration, I have determined it is better for me and my family to depart from public life and try to quickly provide some stability to P&R's leadership for the duration of the Administration," Carson wrote in the email, according to a copy obtained by Military Times.

"I could not be more proud of the work we've achieved together, nor of each of you for the tremendous work that you do," Carson wrote.

It's unclear who Carter might tap to replace Carson for the final nine month of the administration.

A Democrat from Oklahoma who spent four years in the House of Representatives, Carson came to the top Pentagon job after serving as undersecretary of the Army.  His 12 months as the acting personnel chief included several far-reaching changes and accomplishments.

Carson's brief tenure marked a sharp change for the office that for years suffered from high-turnover among its leadership and typically initiated few policy changes. Prior to Carson's appointment last year, most Pentagon personnel reforms from recent years were either initiated by the individual services or by Congress.

The Force of the Future initiative stemmed from the secretary's concern that the military's rigid career tracks may not appeal to the best and brightest among today's younger generation, especially people with high-demand skills needed for career fields like cyber warfare.

Carter has rolled out the policy changes in stages.

In November, Carter unveiled "tranche one," which included:

  • Creating a new high-tech personnel management system for matching individual troops with job assignments, an online network he compared to social media sites like Facebook and Twitter.
  • Creating a new "chief recruiting officer," a civilian to oversee forcewide efforts to attract top talent.
  • Establishing a first-of-its-kind "exit survey" for separating troops to better understand retention trends
  • Expanding corporate fellowship programs to allow service members to work in the private sector.

In January, Carter announced "tranche two," with reforms that included:

  • Extending the forcewide maternity leave benefit to 12 weeks for all women and 14 days for men
  • Expanding mandatory hours for on-base child-care facilities.
  • Expanding options for military service members seeking specific duty stations offering more geographic stability for their families.
  • Coverage for troops seeking to freeze sperm or eggs to preserve fertility options

Carter is now considering formal recommendations for a "tranche three" and tranche four," according to defense officials familiar with the process. That may include:

  • Formally asking Congress to revise the Defense Officer Personnel Management Act, which sets in law many aspects of officer career tracks. That may include scaling back the "up-or-out" rules and joint service requirements as well as other revisions aimed at encouraging officers to pursue non-traditional career paths or develop technical expertise.
  • Revising personnel regulations to make it easier for mid-career professionals from the civilian world to seek "lateral entry" and join the military without having to start at the bottom of the traditional rank and pay structure.