When Gen. Joseph Dunford was selected this spring by President Obama to leave his new job as commandant of the Marine Corps to become the top military officer at the Pentagon, it left a major question: Who would take control of the Marines?

The Marine Corps commandant typically serves in the position for four years, leading the relatively small and close-knit service before retiring. There are virtually no exceptions to that. Gen. James Jones left the post a few months early to become the supreme allied commander of NATO and head of U.S. European Command in 2003, but Dunford is the first sitting commandant to leave and become chairman of the Joint Chiefs of Staff.

The new Marine Corps commandant, Gen. Robert B. Neller, stepped in for Dunford on Thursday, and said he was concerned when he first learned that Dunford would be stepping down as Marine Corps chief to take a new role. Neller said he first learned that would be the case from his wife, D’Arcy, recalling a conversation they had in his office in Norfolk, Va.

“She goes, ‘Who the heck’s going to be the next commandant?” Neller said Thursday, drawing laughter from a crowd assembled on the historic grounds of Marine Barracks Washington. “And I’m like, ‘Damned if I know.'”

Neller, 62, will bring his 40 years of experience as a Marine infantry officer to the position. He last served as the head of Marine Corps Forces Europe and Marine Corps Forces Command in Norfolk, Va., which oversees and provides Marines for deployments overseas. He commanded troops in Iraq from late 2005 until early 2007, and deployed earlier in his career to Panama in 1989 as part of Operation Just Cause, in which Manuel Noriega was deposed, and to Somalia in 1993 as part of Operation Restore Hope.

Neller said he will execute the plan Dunford laid out for the service, possibly with a “few slight deviations,” and to ask Congress only for what the service needs, rather than what it wants. Dunford’s plan called for emphasizing a realignment of troops to meet demands in the Pacific and Africa, coordinating better with Special Operations units and preparing for deployments in an “anti-access, area denial” environment, in which enemies can contest U.S. troops with a variety of weapons.

“I remember what the Marine Corps was like 40 years ago,” Neller said. “We had good Marines, but I’d put this group up against anybody back then. And so now it’s the challenge to make this go forward.”

Neller released his first message to his troops afterward, saying in a two-page letter that rank-and-file Marines should expect from their leaders firm but fair leadership, accountability, realistic training, cutting-edge weapons and equipment, opportunities for advancement, care and support for families and wounded service members, and honesty, integrity and compassion.

Marine leaders, in turn, should expect those serving in the Marine Corps to give 100 percent of themselves, understand their profession, show accountability, care for their equipment, overcome adversity, tell the truth, set new goals and earn trust, Neller wrote.

The “Passage of Command” ceremony on Thursday was attended by dozens of current and retired Marine generals, Defense Secretary Ashton B. Carter and Navy Secretary Ray Mabus. Several current and former members of Congress also attended, including former Sen. Jim Webb (D.-Va.), a presidential candidate and Marine veteran. Dunford told the crowd, seated on bleachers between the brick buildings of the barracks, that he feels fortunate Neller was selected.

“Just like all of the other Marines and sailors, I now have the good fortune to have a leader who is passionate,” Dunford said. “He’s compassionate. He’s got extraordinary operational credibility. But as importantly in the position he has just assumed, he has the energy and vision to take us into the future.”

Carter called Neller a tested warrior and innovative strategist who never hesitates to act and always is planning ahead.

“Like Bob says, if we want to win, we can’t just show up,” Carter said of Neller. “I agree. Bob’s leadership will help us stay ahead in keeping our Marines the world’s unrivaled expeditionary rapid response force. And in building the force of the future, where we continue to be the best, by attracting and retaining the best America has to offer.”