The Pentagon has given the Department of Homeland Security permission to test a military-grade heat ray and develop tactics to potentially use it in operations at the southern US border, according to a memo signed by Defense Secretary Pete Hegseth last month and obtained by CNN.

The heat ray, officially known as the Active Denial System, is a nonlethal weapon that shoots an invisible beam of electromagnetic waves that can reach a little more than half a mile away, according to the US military.

The energy beam causes a burning sensation when it comes into contact with the human skin — which Pentagon officials have previously compared to feeling a blast of heat when opening a hot oven. Military officials have said the resulting “tingling effect” lasts between 10 and 15 minutes but also generates “an instinctive and irresistible urge to run from the effect.”

Deploying the heat ray at the US border would be an unprecedented step, even for the Trump administration, which has made border security and clamping down on immigration a top priority. The DHS request did not specify where or how the weapon would be tested and how it might eventually be used, but over the years, there have been internal discussions about potentially using it for crowd dispersal along the US-Mexico border, according to current and former Customs and Border Protection officials.

US officials had also considered deploying the system during moments of domestic unrest, including at the end of President Donald Trump’s first term when protests erupted over the murder of George Floyd, according to a former US official familiar with those discussions.

The memo authorizes the “temporary loan” of one ADS system for seven months, starting in September, and states that it “shall not be operated by DoW (Department of War) personnel,” appearing to absolve the Pentagon of any responsibility for how the directed-energy system may ultimately be deployed.

It also states that DHS is solely responsible for “system employment, use and development of tactics, techniques and procedures.” At the end of the seven-month loan period, DHS can submit an additional request for further use of the Pentagon system in border operations based on need, a defense official told CNN.

“CBP is continually evaluating new technologies, especially those that enhance operational effectiveness and strengthen mission capabilities,” a Customs and Border Protection spokesperson said in a statement to CNN.

The Pentagon referred CNN to DHS when asked for comment.

The US military briefly deployed the system to Afghanistan nearly two decades ago but ultimately declined to use it during active combat operations. The US military also considered using the system for crowd control purposes at US facilities abroad where terrorist detainees were being held at the time but ultimately declined to employ it for that purpose as well, according to a source familiar with those previous internal considerations.

Customs and Border Protection officials have previously entertained the idea of using the system in areas where there’s a high concentration of illegal crossings. Border officials have occasionally discussed potentially using the system as a crowd dispersal tool, but it has never been deployed.

Officials ran into hurdles over legalities, use of force, effectiveness, and potential issues over sovereignty, particularly if the system was deployed on people in Mexico who had not yet crossed into the US. Chief among those concerns, however, was whether people could be harmed, either directly or indirectly, by the weapon.

“Even if they’re chasing people back to the river, you don’t want them to go in and drown,” a former CBP official told CNN. “For the cost, for the training and for the policies you’re going to create, is the juice worth the squeeze?”

El Centro sector, which covers around 70 miles along the US-Mexico border, evaluated the system several years ago, when Rodney Scott, who now serves as CBP commissioner, helmed that sector, according to a CBP official.

At the time, officials were discussing whether the system might help agents with an influx of illegal crossings along the nearby river by discouraging people from trying to cross in that area or pushing them to get out of the water.

One of the considerations at the time was whether the system might result in more rescues if people were incapacitated by the technology, the official said, though it’s unclear why it wasn’t deployed.

In 2018, prior to midterms, CBP officials also weighed using it against migrants, but then-Homeland Security Secretary Kirstjen Nielsen shot it down.

“The issue was treating immigrants and citizens like enemy combatants,” a former DHS official familiar with previous discussions about using the weapon against migrants told CNN. “Thematically, inhumane treatments typically get rejected.”

Some Border Patrol agents have more recently cast doubt over whether they need the tool at all amid low border crossings and an increase in personnel, according to another former CBP official.