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WASHINGTON (Reuters) - Former U.S. Defense Secretary Jim Mattis rejoined the board of General Dynamics Corp GD.N on Wednesday, seven months after quitting his job in the Trump administration over disagreements about foreign policy, the defense contractor said.

Mattis, a retired Marine general, had served on General Dynamics’ board but resigned in 2017 to take the top job at the Pentagon after being nominated by U.S. President Donald Trump.

Mattis resigned from the Defense Department in December after clashing with Trump on issues such as the president’s abrupt decision to pull troops out of Syria and Afghanistan.

“Jim is a thoughtful, deliberate and principled leader with a proven track record of selfless service to our nation,” said General Dynamics Chairwoman and Chief Executive Phebe Novakovic in a statement. “We are honored to have him on our board.”

The Trump administration has been a revolving door for industry executives serving in the government. Former Deputy Defense Secretary Patrick Shanahan, who filled the role as acting secretary after Trump pushed Mattis out early, was a Boeing Co BA.N executive.

Recently confirmed Defense Secretary Mark Esper is a former lobbyist for weapons company Raytheon Co RTN.N.

Mattis was often at odds with Trump on major policy points. He reassured North Atlantic Treaty Organization allies in 2017 that it was “the most successful and powerful military alliance in modern history” after Trump questioned the need for the organization.

His resignation was met with discomfort on Capitol Hill from Republicans and Democrats. Senate Majority Leader Mitch McConnell said in a statement at the time he was “particularly distressed” that Mattis was resigning over sharp differences with the president.

Mattis will not engage in lobbying to the Pentagon for at least five years after his departure from the government, according to an ethics pledge issued in a Trump executive order.