Acting Defense Secretary Patrick Shanahan took up the reins of the US armed forces Tuesday by praising his predecessor, newly ousted Jim Mattis, and seeking to reassure the country that it remains safe.

“Under the direction of President Trump, the Department of Defense remains focused on safeguarding our nation,” Shanahan said in a statement released on New Year’s Day.

“We have deep respect for Secretary Mattis’ lifetime of service, and it has been a privilege to serve as his deputy secretary,” he continued.

“As acting secretary of defense, I now look forward to working with President Trump to carry out his vision alongside strong leaders including the service secretaries, the Joint Chiefs of Staff, the combatant commanders, and senior personnel in the Office of the Secretary of Defense.”

On Dec. 20, a day after Trump abruptly called for the withdrawal of US troops from Syria, Mattis announced he would step down – writing a two-page letter of resignation in which he rebuked the president’s defense and foreign policies.

The retired four-star Marine general initially planned to resign at the end of February to allow Trump time to find a replacement, but the president later announced that Mattis would leave on Jan. 1 instead.

Trump then named Shanahan, a former Boeing executive with scant government and foreign policy experience, as the acting defense secretary.

In his farewell memo Monday, Mattis encouraged all Defense Department employees to “keep the faith and hold fast.”

“Our Department’s leadership, civilian and military, remains in the best possible hands,” wrote Mattis, who had been widely regarded as a moderating force against the president’s volatility.

In his statement Tuesday, Shanahan added: “The Department of Defense continues to be one of our nation’s bedrock institutions. Our foundational strength lies in the remarkable men and women who volunteer to serve our country and protect our freedoms, while making immense personal sacrifice.

“It is an honor to work with such a dedicated team committed to the greatness of our nation.”