While Americans on the East Coast are toasting the arrival of the new year, current Secretary of Defense James Mattis will be on a conference call with Pentagon officials to turn over authority to Deputy Defense Secretary Patrick Shanahan. Shanahan will serve as acting Defense Secretary until President Donald Trump appoints a new permanent replacement.

The phone call will suffice as the formal transition of power within the Pentagon, as the role does not require a swearing-in ceremony of any sort. Neither Mattis nor Shanahan need to be physically present for the transition of power, but the call itself is meant to be a symbolic one. At midnight Monday night, Mattis will relinquish the reigns of the American defense apparatus and the call will serve as a punctuation mark that clarifies to everyone within the Pentagon’s purview that Shanahan is now in charge.

“The position of the secretary of defense is a command position, and the purpose of the call is to ensure all members within the government know who is in command,” read a Pentagon statement released earlier this week. “Once the phone call is complete, the Department of Defense will notify the White House that Mr. Shanahan has assumed the authority of the acting secretary of defense.”

Shanahan, a former Boeing executive with no military or government experience, may find himself in the role for a while, despite the “acting” prefix on his title. The list of potential replacements for Mattis was never particularly long under Trump’s administration, but it grew considerably shorter in recent weeks following the president’s announced pull-out of both Syria and Afghanistan. Even prominent conservative voices that have historically served as an ally to Trump have removed themselves from the running by making vocal criticisms of what has been characterized as a military pull-out without any actual strategy.