Dec. 23 (UPI) -- President Donald Trump announced Sunday that Patrick Shanahan will take on the role of acting secretary of defense at the start of the new year -- two months ahead of Jim Mattis' planned retirement.
Trump wrote on Twitter that Shanahan, who had been serving as current Defense Secretary Jim Mattis' deputy, will step into the role on Jan. 1, two months earlier than Mattis was scheduled to depart after submitting his resignation to the White House Thursday.
"Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!" Trump wrote.
Pentagon spokesman Army Col. Rob Manning issued a statement regarding the secretary of defense position without addressing the the change, the Washington Post reported.
"The secretary of defense serves at the pleasure of the president," Manning said. "The department remains focused on national security."
Mattis wrote in his resignation letter that he would depart the office on Feb. 28, citing disagreements about how the United States should be involved in international issues including withdrawing troops from Syria.
"You have the right to have a secretary of defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position," he wrote.
Trump commented on the situation in Syria on Saturday, following the announcement of Mattis' departure.
"If anybody but your favorite President, Donald J. Trump, announced that, after decimating ISIS in Syria, we were going to bring our troops back home (happy & healthy), that person would be the most popular hero in America. With me, hit hard instead by the Fake News Media. Crazy!" he wrote on Twitter.
Shanahan worked as an executive for Boeing for decades prior to joining the Trump administration and oversaw the audit as well as its development of a new missile defense policy.