Secretary of Defense Ash Carter on Monday announced the shuffling of several senior civilian Pentagon officials ahead of Army Secretary John McHugh leaving office before November. 

Eric Fanning, who has served as Carter’s chief of staff since taking office in February, has been named undersecretary of the Army. The position has been vacant since Brad Carson became acting secretary of defense for personnel and readiness. Fanning previously served as both deputy secretary of the Navy and as acting secretary of the Air Force before being tapped as Carters top advisor.

“One of my first decisions upon returning to the Pentagon was asking Eric Fanning to serve as my chief of staff,” Carter said in a statement. “His deep wells of knowledge and vast experience in the Pentagon … have been crucial assets for my front office. He has also helped me build an outstanding team of civilian and military leaders across the Pentagon. Working with him closely over the last several months, I’ve seen first-hand why he is one of the most respected appointees in the Obama administration.”

Fanning will be the principal aide to McHugh as he winds down his tenure prior to Nov. 1. He then will be the Army’s top civilian until a replacement for McHugh is confirmed and sworn in.

Carson has taken lead on Carter’s Force of the Future initiative, which is aimed at retaining skilled personnel, compensating them fairly, recruiting top-notch talent and maintaining the Army’s relevance beyond the wars of the past 13 years.

“I will forever be grateful for Eric’s advice and leadership during this crucial first phase of my time as secretary of defense, and look forward to continuing to work with him as he helps lead the men and women of the world’s most powerful ground force,” Carter said.

Carter’s current Deputy Chief of Staff Eric Rosenbach will be promoted to chief of staff, effective July 6. A former Army intelligence officer and Harvard faculty member, Rosenbach has served multiple roles at the Pentagon, the most senior of which was as assistant secretary of defense for homeland defense and global security. In that role, Rosenbach was the “principal architect” of the Defense Department’s cyber security policy.

“I am confident that Eric brings the right blend of strategic acumen, technological expertise, and managerial skill to help me lead the department during an important time in its history,” Carter said. “I would like to thank both Eric’s, as well as their families, for being willing to serve in these positions.”