Military units from across the country are scrambling to get in place along the southern border following President Donald Trump's order earlier this week^[1], and U.S. aircraft have already begun flying deported immigrants out of the country as the mission rapidly moves along.

After the Department of Defense announced Wednesday that 1,500 troops would be initially assigned to the border mission, what bases and units they were coming from and what other forces could be included remained questions.

By Friday, U.S. Northern Command -- which was tasked with overseeing the mission -- began to provide some details but noted in a statement that "the exact number of personnel will fluctuate as units rotate personnel and as additional forces are tasked to deploy once planning efforts are finalized."

Read Next: Problems with Tricare Contract Transition 'Actively Harming' Military, Lawmaker Tells Pentagon^[2]

Since Trump issued his executive order to use even more active-duty troops to secure the border late Monday, the Pentagon -- largely led by placeholder officials -- has moved fast to comply with the presidential mandate, which set aggressive deadlines for military planners.

During that effort, officials have struggled to articulate many of the details that are normally a fundamental part of any military deployment^[3], even as this one reportedly could ultimately swell to as many as 10,000 troops ^[4]and as service members were already beginning to head to the border.

"If you see in the executive order, the 30-day timeline for a Level 3 plan, that's an incredibly aggressive timeline," an official from U.S. Northern Command, or NORTHCOM, told Military.com on Friday. "Level 3" refers to plans that are one step below a fully formed operational document^[5].

They noted that plans like that "usually take way longer to come together, so it's all hands on deck."

Multiple service and command officials spoke to Military.com on condition of anonymity to explain details of a rapidly evolving military situation.

On Wednesday afternoon, the Pentagon held its first briefing to offer details about the initial wave of 1,500 troops being mobilized to the southern border.

While reporters were told that the breakdown would be 1,000 soldiers from the Army^[6] and 500 Marines, the senior defense official who spoke to reporters stressed that it was just "36 hours after the [executive order], so that's something to keep in mind." No details about what units would be tapped were offered.

That evening, a Marine Corps^[7] official told Military.com that 500 Marines from 1st Marine Division out of Camp Pendleton^[8], California, were prepared to respond to the border, with preparations in place to surge that number to up to 2,500 personnel if called upon to do so.

It would take until Friday for NORTHCOM to offer the same level of detail for the Army when, in a statement, the combatant command named 13 Army units from Texas, Kentucky, New York, Georgia, Kansas, Colorado and Washington state making up the 1,000 soldiers, as well as the battalions and units that comprise the 500 Marines being deployed.

Pentagon officials also told reporters Wednesday that all 500 Marines were being pulled from the Federal Emergency Management Agency mission to support California's wildfire response. But on Friday, the Marine Corps clarified to Military.com that, while a "majority" of the Marines being sent to the border had previously been tapped to respond to wildfires in California, "there are a few exceptions to that," including shifting certain capabilities and replacing Marines coming up on the end of their service contracts.

Amid this fluid situation was also an order from Acting Defense Secretary Robert Salesses to the services to pause all social media use though, in a statement Thursday, he did say that the "pause does not apply for content and imagery relative to the DoD's current border security operations."

Marines Move Out

While officials were hesitant to offer early details on which specific units were actually heading the border, images of the response effort were already being made available online.

Marines were photographed laying concertina wire^[9] at the border as early as Thursday and, on Friday, the White House posted a video on social media^[10] of Marine Corps MV-2B Ospreys^[11] landing and offloading Marines at what appeared to be the border with Mexico as agents from the U.S. Border Patrol looked on.

Another Marine Corps official told Military.com that an initial element of about 50 Marines arrived early Thursday morning in San Diego, which is about 30 minutes north of California's southern border. They said that roughly 450 other Marines from the unit, specifically detachments from 1st Combat Engineer and 7th Combat Engineer battalions, were staged and ready to move from Camp Pendleton -- further north in the state -- once staging areas were set.

As of Friday afternoon, all 500 Marines who staged at Camp Pendleton were at the border, a Marine Corps official told Military.com.

Two Ospreys from the 3rd Marine Aircraft Wing out of Marine Corps Air Station Miramar^[12], near San Diego, reconnoitered landing zones at California's southern border Thursday afternoon, another Marine Corps official told Military.com on Friday.

Marines with VMM-161 and MWSS-373, Osprey and aviation ground support squadrons, all belonging to 3rd MAW, met with Border Patrol agents on the ground before returning to MCAS Miramar as part of an effort to scout potential landing areas for delivering supplies and personnel if necessary for future operations, according to two Marine officials.

Army's Rapid Response Force

Multiple military officials also told Military.com that the 82nd Airborne's 3rd Brigade Combat Team -- one of the nation's most visible units and the military's rapid response force -- is also preparing to deploy to the southern border.

The use of the 82nd Airborne is significant since the unit is typically used to respond to major military crises that threaten U.S. troops, citizens or allies abroad. In recent years, it has been tapped to respond to escalating tensions with Iran^[13], put on alert and deployed to Europe ahead of the Russian invasion of Ukraine^[14], and took part in the U.S. withdrawal from Afghanistan.

Officials also said that part of the 10th Mountain Division out of Fort Drum^[15] in New York may serve as a headquarters element for the response at the border.

However, officials at the Pentagon were not ready to make the announcement Friday.

"At this time, there are no units from the 82nd Airborne Division or the 10th Mountain Division mobilizing to support the mission at the southern border," a defense official told Military.com, but they added that the Pentagon was "actively planning and assessing the situation."

The Washington Post reported Friday^[16] that one plan under consideration was a dramatic and public road march of Stryker^[17] armored combat vehicles to the border.

Air Force Repatriation Flights

Meanwhile, Air Force^[18] C-17 Globemaster IIIs^[19], one from the 60th Air Mobility Wing out of Fort Bliss^[20], Texas, and another out of Tuscon, Arizona, according to photo captions, were flying immigrants out of the country as recently as Wednesday evening. The Department of Homeland Security provided officers for the flight.

U.S. Transportation Command is leading the Air Force's airlift efforts for the border mission.

"We can confirm that overnight two Air Force C-17s conducted repatriation flights from the U.S. to Guatemala," a defense official confirmed to Military.com.

Images of the deportation flights were posted by the Department of Defense on Wednesday. Additionally, images of UH-72 Lakota^[21] helicopters preparing for and operating surveillance flights out of New Mexico were also broadcast.

"This is just the beginning of something more and something new," the NORTHCOM official told Military.com on Friday, adding that the combatant command was "in the middle of an aggressive 30-day planning effort that will be looking across domains and across components to provide the solution of securing the border."

"This is the sole focus of the NORTHCOM planners, and they're not only looking at the comfortable domain of land, we are looking at land, maritime, air, cyber -- everything."

-- Steve Beynon contributed to this report.

Related: Trump Orders 1,500 Active-Duty Troops to Border Ahead of Pentagon Security Plan Deadline^[22]

WASHINGTON — Sen. Lisa Murkowski announced Thursday that she will vote against confirming Pete Hegseth^[1] to lead the Pentagon, becoming the first Republican to oppose one of President Donald Trump’s^[2] Cabinet picks ahead of a crucial test vote.

Murkowski, of Alaska, said in a lengthy statement that allegations of excessive drinking and aggressive actions toward women^[3], which Hegseth has denied, show that his behaviors “starkly contrast” with what is expected of the U.S. military. She also noted his past statements that women should not fill military combat roles.

“I remain concerned about the message that confirming Mr. Hegseth sends to women currently serving and those aspiring to join,” Murkowski wrote on social media.

Murkowski said behavior that Hegseth has acknowledged, “including infidelity on multiple occasions,” shows a lack of judgement. “These behaviors starkly contrast the values and discipline expected of service members,” she said.

"Above all, I believe that character is the defining trait required of the Secretary of Defense, and must be prioritized without compromise,” she said.

Senate GOP leaders rushed to advance Trump's^[4] defense secretary nominee toward confirmation, despite grave objections from Democrats and stirring unease among Republicans over his behavior and qualifications to lead the U.S. military.

It will take a simple majority senators to advance Hegseth’s confirmation in Thursday’s vote. Most Republicans, who hold a 53-seat majority in the chamber, have signaled they will back the nominee, though Vice PResident JD Vance could be called in to break a tie vote.

Rarely has a Cabinet choice encountered such swirling allegations of wrongdoing. Trump is standing by Hegseth, and the chairman of the Senate Armed Services Committee has dismissed the claims as factually inaccurate.

“I am ironclad in my assessment that the nominee, Mr. Hegseth, is prepared to be the next secretary of defense,” the chairman, Sen. Roger Wicker, R-Miss., said in a statement on the eve of the test vote. "The Senate needs to confirm this nominee as fast as possible.”

A new president's national security nominees are often the first to be lined up for confirmation, to unsure U.S. safety at home and abroad. Already the Senate has overwhelmingly confirmed Marco Rubio^[5] as secretary of state in a unanimous vote, and it was on track to confirm John Ratcliffe^[6] as CIA director later Thursday.

But Hegseth stands in a category of his own amid allegations^[7] that he sexually assaulted a woman at a Republican conference in California, which he has denied as a consensual encounter, and of heavy drinking at events when he led a veterans organization. He has also said women should not work in combat roles, a view he has since tempered during his confirmation process.

A new claim emerged^[8] this week in an affidavit from a former sister-in-law who claimed Hegseth was abusive to his second wife to the point that she feared for her safety. Hegseth has denied the allegation. In divorce proceedings, neither Hegseth nor the woman claimed to be a victim of domestic abuse.

Senate Democratic Leader Chuck Schumer said Thursday that Hegseth is unqualified for the job because of his personal behavior, including drinking, and his lack of experience.

“One of the kindest words that might be used to describe Mr. Hegseth is erratic, and that’s a term you don’t want at DOD,” Schumer said. “He has a clear problem of judgment.”

A Princeton and Harvard-educated former combat veteran, Hegseth went on to make a career at Fox News, where he hosted a weekend show. Trump tapped him as the defense secretary to lead an organization with nearly 2.1 million service members, about 780,000 civilians and a budget of $850 billion.

Hegseth has promised not to drink on the job if confirmed.

But senators have remained doubtful of his experience and abilities and the alleged behavior that could lead to reprimand or firing^[9] for military personnel he would now be expected to lead.

Sen. Joni Ernst, R-Iowa, herself a combat veteran and sexual assault survivor, has signaled her backing.

However, several GOP senators, including Murkowski and Sen. Susan Collins of Maine, are being widely watched for their votes.

During a fiery confirmation^[10] hearing, Hegseth swatted away allegations of wrongdoing one by one — dismissing them as “smears” — as he displayed his military credentials and vowed to bring “warrior culture" to the top Pentagon post.

Wicker said he had been briefed a third time on the FBI background investigation into Hegseth. He said "the allegations unfairly impugning his character do not pass scrutiny.”

WASHINGTON — The Senate advanced the nomination of Pete Hegseth as President Donald Trump's defense secretary Thursday on a largely party-line vote, despite grave objections from Democrats and stirring unease among Republicans over his behavior and qualifications to lead the U.S. military.

Two Republicans, Sen. Lisa Murkowski of Alaska and Sen. Susan Collins of Maine, broke ranks with Trump and his allies who have mounted an extensive public campaign to push Hegseth toward confirmation. The former combat veteran and Fox News host faces allegations of excessive drinking and aggressive actions toward women, which he has denied. The vote was 51-49, with a final vote on confirmation expected Friday.

Senate Democratic Leader Chuck Schumer implored his colleagues to think seriously, "Is this the best man we have to lead the greatest military in the world?"

Murkowksi, in a lengthy statement, said that his behaviors "starkly contrast" with what is expected of the military. She also noted his past statements that women should not fill military combat roles. Hegseth sought to temper those statements during the confirmation process.

"I remain concerned about the message that confirming Mr. Hegseth sends to women currently serving and those aspiring to join," Murkowski wrote on social media.

Murkowski said behavior that Hegseth has acknowledged, "including infidelity on multiple occasions," shows a lack of judgment. "These behaviors starkly contrast the values and discipline expected of service members," she said.

Collins said that while she appreciates Hegseth's "courageous military service and his ongoing commitment to our service members and their families, I am concerned that he does not have the experience and perspective necessary to succeed in the job."

She also said that after a lengthy discussion with Hegseth, "I am not convinced that his position on women serving in combat roles has changed."

Rarely has a Cabinet choice encountered such swirling allegations of wrongdoing. Trump is standing by Hegseth, and the chairman of the Senate Armed Services Committee has dismissed the claims as factually inaccurate.

It will take a simple majority of senators to confirm Hegseth's nomination. Most Republicans, who hold a 53-seat majority in the chamber, have signaled they will back the nominee, though Vice President JD Vance could be called in to break a tie vote.

"I am ironclad in my assessment that the nominee, Mr. Hegseth, is prepared to be the next secretary of defense," the chairman, Sen. Roger Wicker, R-Miss., said in a statement on the eve of voting. "The Senate needs to confirm this nominee as fast as possible."

A new president's national security nominees are often the first to be lined up for confirmation, to ensure U.S. safety at home and abroad. Already the Senate has overwhelmingly confirmed Marco Rubio as secretary of state in a unanimous vote, and confirmed John Ratcliffe as CIA director Thursday.

But Hegseth stands in a category of his own amid allegations that he sexually assaulted a woman at a Republican conference in California, which he has denied as a consensual encounter, and of heavy drinking at events when he led a veterans organization.

A new claim emerged this week in an affidavit from a former sister-in-law who claimed Hegseth was abusive to his second wife to the point that she feared for her safety. Hegseth has denied the allegation. In divorce proceedings, neither Hegseth nor the woman claimed to be a victim of domestic abuse.

Schumer said Thursday that Hegseth is unqualified for the job.

"One of the kindest words that might be used to describe Mr. Hegseth is erratic, and that's a term you don't want at DOD," Schumer said. "He has a clear problem of judgment."

A Princeton and Harvard-educated former combat veteran, Hegseth went on to make a career at Fox News, where he hosted a weekend show. Trump tapped him as the defense secretary to lead an organization with nearly 2.1 million service members, about 780,000 civilians and a budget of $850 billion.

During a fiery confirmation hearing, Hegseth swatted away allegations of wrongdoing one by one — dismissing them as "smears" — as he displayed his military credentials and vowed to bring "warrior culture" to the top Pentagon post.

Hegseth has promised not to drink on the job if confirmed.

Wicker said he had been briefed a third time on the FBI background investigation into Hegseth. He said "the allegations unfairly impugning his character do not pass scrutiny."

But senators have remained doubtful of his experience and abilities and the alleged behavior that could lead to reprimand or firing for military personnel he would now be expected to lead.

Still, Sen. Joni Ernst, R-Iowa, herself a combat veteran and sexual assault survivor, has signaled her backing.