The president has directed the U.S. military to reinforce the border, and the acting secretary of defense on Wednesday announced the Pentagon is sending around 1,500 active duty troops to the country’s southern border, joining 2,500 active duty personnel already there.

The U.S. military's mission on the border is moving quickly as the White House and the Pentagon are making it a priority to publicize news about the mission.

The U.S. Pentagon is sending an additional 1,500 active-duty troops to the southern border by the end of the week, a senior U.S. military official told Fox News.

The I Marine Expeditionary Force is made up of about 53,000 active-duty troops, who are primarily stationed at Camp Pendleton, as well as at Marine Corps Air Stations Miramar and Yuma, and the Marine Corps Air/Ground Combat Center at 29 Palms, California.

A U.S. Border Patrol agent killed during a traffic stop near the Canadian border worked security duty at the Pentagon during the time of the Sept. 11 attacks.

The Pentagon will begin deploying as many as 1,500 ... Get top local stories in San Diego delivered to you every morning. Sign up for NBC San Diego's News Headlines newsletter.

The first such military flight out of El Paso, Texas, took place, bound for Guatemala with approximately 80 immigrants on board.

The Senate on Thursday voted to advance Pete Hegseth's nomination to be President Donald Trump's defense secretary, putting him on a path to final confirmation at the end of the week.

The Pentagon said it has begun deploying 1,500 active duty troops to the southern border, including 500 Marines from Camp Pendleton.

WASHINGTON (AP) — It is unclear who will take over at the Pentagon and the military services when the top leaders all step down Monday as President-elect Donald Trump is sworn into office.