Almost four months after the Senate first received his nomination to be the top civilian in the Department of the Army, former Raytheon executive Mark Esper took his oath of office Tuesday.

Esper, a West Point graduate and former lieutenant colonel, will join Army Undersecretary Ryan McCarthy, who had been serving as the acting secretary since his own August swearing-in, on an ambitious line-up of initiatives that includes reforming the Army’s notoriously slow — and often wasteful — procurement process.

“Thanks to your service, our Army remains the world’s premier ground combat force and the bedrock of our nation’s defense,” Esper wrote in a Tuesday letter addressed to the force. “This is why the readiness and welfare of our soldiers, civilians and their families will always be foremost in my mind, and why I intend to pursue initiatives that will offer the professional opportunities and quality of life all deserve.“

His top priorities will be readiness, modernization and a commitment to Army values, Esper wrote.

“This includes treating everyone with respect, collaborating broadly, and always doing the right thing,” he wrote. “The Army is at its best when it works and fights as one team, and with the challenges we face ahead, a recommitment to these values will serve us well.”

Esper, whom the Senate confirmed on Nov. 15, succeeds former Army Secretary Eric Fanning, who left with the outgoing Obama administration in January.

Esper is President Trump’s third Army secretary nominee. The previous candidates, Tennessee State Senator Mark Green and businessman Vincent Viola, dropped out because of political controversy and an inability to untangle conflicting business interests, respectively.

Esper’s nomination hearing and confirmation vote had been delayed for months by summer recesses and a Pentagon-Senate battle over the Defense Department’s communication about policy and operational decisions.

“We owe our young men and women in uniform leadership that fits their service,” Sen. John McCain, R-Arizona said before the vote. “I’m confident that [Esper] will provide our Army with that leadership. His record of service in the Army, in the Pentagon and on Capitol Hill provides the foundation for the leadership our soldiers deserve.”