WASHINGTON — The Pentagon said Wednesday it has begun deploying 1,500 active-duty troops to help secure the southern border, putting in motion plans President Donald Trump laid out in executive orders shortly after he took office to crack down on immigration. Acting Defense Secretary Robert Salesses said the troops will fly helicopters to assist Border Patrol agents and help in the construction of barriers. The Pentagon also will provide military aircraft for Department of Homeland Security deportation flights for more than 5,000 detained migrants. The number of troops and their mission may soon change, Salesses said in a statement. “In short order, the department will develop and execute additional missions in cooperation with DHS, federal agencies, and state partners to address the full range of threats outlined by the President at our nation’s borders,” Salesses said. Defense officials added that the department is prepared to provide more troops if asked, including up to 2,000 more Marines. The U.S. forces manning helicopters, the crews for the military transport planes and the intelligence analysts being assigned to the border will be in addition to the 1,500, according a senior military official and a senior defense official who briefed reporters on the condition of anonymity to provide additional details on the deployment. The military helicopters have already gone into action, flying six sorties on Wednesday, the senior U.S. military official. “We also anticipate there could be some additional airborne intelligence surveillance support assets … for increased situational awareness,” the official said. U.S. military drones could be brought in to assist with surveillance of the southern border. “That is still not fully decided yet” the senior U.S. military official said. “We’re waiting to refine what the requirement is, working with NORTHCOM,” the U.S. Northern Command. It is unclear if the troops will be armed. The senior military official said that decision is typically left to the commander of NORTHCOM. “As of right now, none of the forces that we’re sending there are intended to be used for law enforcement” the senior military official said. Officials said there was no plan now for the troops to perform law enforcement duties, which would put them in a dramatically different role for the first time in decades. Any decision on this would be made by the White House, they said. The active-duty forces will join the roughly 2,500 U.S. National Guard and Reserve forces already there. Until this deployment, there were no active-duty troops working along the roughly 2,000-mile border. A couple of hundred troops started moving to the border earlier Wednesday, the officials said. The troops will include 500 Marines from Camp Pendleton in California, and the remainder will be Army. The U.S. forces being used for the deportation flights are in addition to the 1,500 deployed for the border mission. Those flights will involve four Air Force aircraft — C-130s and C-17s — based in San Diego and El Paso, along with crews and maintenance personnel. Troops have performed similar duties in support of Border Patrol agents in the past, when both Trump and former President Joe Biden sent active-duty troops to the border. Troops are prohibited by law from doing law enforcement duties under the Posse Comitatus Act, but that may change. Trump has directed through executive order that the incoming secretary of defense and incoming homeland security chief report within 90 days if they think an 1807 law called the Insurrection Act should be invoked. That would allow those troops to be used in civilian law enforcement on U.S. soil. The last time the act was invoked was in 1992 during rioting in Los Angeles in protest of the acquittal of four police officers charged with beating Rodney King. Military personnel have been sent to the border almost continuously since the 1990s to help address migration, drug trafficking and transnational crime. In his first term, Trump ordered active-duty troops to the border in response to a caravan of migrants slowly making its way through Mexico toward the United States in 2018. More than 7,000 active-duty troops were sent to Texas, Arizona and California, including military police, an assault helicopter battalion, various communications, medical and headquarters units, combat engineers, planners and public affairs units. At the time, the Pentagon was adamant that active-duty troops would not do law enforcement. So, they spent much of their time transporting Border Patrol agents to and along the border, helping them erect additional vehicle barriers and fencing along the border, assisting them with communications and providing some security for border agent camps. The military also provided Border Patrol agents with medical care, pre-packaged meals and temporary housing. It also was not yet clear if the Trump administration will eventually order the military to use bases to house detained migrants. The defense officials said such a request has not been made as of yet. Bases previously have been used for that purpose, and after the 2021 fall of Kabul to the Taliban, they were used to host thousands of Afghan evacuees. The facilities struggled to support the influx. In 2018, then-Defense Secretary Jim Mattis ordered Goodfellow Air Force Base in San Angelo, Texas, to prepare to house as many as 20,000 unaccompanied migrant children, but the additional space ultimately wasn’t needed and Goodfellow was determined not to have the infrastructure necessary to support the surge. In March 2021, the Biden administration greenlighted using property at Fort Bliss, Texas, for a detention facility to provide beds for up to 10,000 unaccompanied migrant children as border crossings increased from Mexico. The facility, operated by DHS, was quickly overrun, with far too few case managers for the thousands of children that arrived, exposure to extreme weather and dust and unsanitary conditions, a 2022 inspector general report found. VOA National Security Correspondent Jeff Seldin contributed to this report.