The electric-shock gloves immigration agents could soon use to control detainees and protesters worked so powerfully during a military exercise that participants felt intense pain, stopped fighting immediately and feared additional exposures, according to a previously unreleased army study.

Immigration and Customs Enforcement (ICE) leaders were aware of the findings before signing a $16.7m contract in August to purchase 6,000 pairs of shock gloves, according to records obtained by the watchdog group American Oversight and shared with the Associated Press.

The shocks had a profound impact on army employees who played the role of combative prisoners during the exercise, which took place at the military prison at Fort Leavenworth in Kansas in October 2024 – as the Biden administration was in its final months.

The participants, several of whom were large-statured men, stopped resisting seconds after officers applied shocks by touching gloves to their skin, and were left with “fatigue, soreness and excessive apprehensiveness to being shocked again”, the study found.

The gloves carry the brand name G.L.O.V.E., which stands for Generated Low Output Voltage Emitter, and are manufactured by Compliant Technologies, a company owned by military veterans and based in Lexington, Kentucky.

When it emerged that the second Trump administration was ordering the devices for ICE, amid a hardline anti-immigration crackdown and record arrests and detention of immigrants the government wants to deport, experts expressed alarm and pointed to some high-profile lawsuits over their use in local correctional facilities.

In one extreme case, a 43-year-old man died after allegedly being shocked 40 times by officers with a combination of the gloves and a Taser in a county jail in Kentucky, and the man’s widow is suing authorities.

In the previous military exercise, the authors of the study shared with AP said: “After experiencing the effects of the GLOVE … participants stated just seeing the GLOVE was enough to make them want to comply.”

ICE has called the gloves “distraction and de-escalation devices” that will be safer than other non-lethal options to subdue targets for arrest and deportation and protesters who create civil disturbances. The agency has argued the rapid compliance they cause will keep officers safer and prevent incidents from requiring potentially lethal force.

But critics have warned the gloves will give ICE another weapon to intimidate and brutalize people even as the agency is under fire for excessive force that has left a trail of deaths and injuries across the nation.

“The military assessment in ICE’s own files shows that these gloves can cause ‘intense pain’ and force compliance. It does not establish that they are safe,” said Chioma Chukwu, executive director of American Oversight. “Everyone should be alarmed that ICE is preparing to deploy a tool designed to inflict, at best, intense pain, without showing that it is safe for the people who will be subjected to it.”

ICE released the study and other documents to American Oversight as part of the group’s Freedom of Information Act lawsuit against the agency seeking records related to its use of force.

The military prison study assessed whether the gloves could be used effectively to forcibly remove combative prisoners from their cells, to respond to disturbances in common areas and to transport uncooperative inmates. Role-playing employees conducted several scenarios with and without the gloves to test their impact, including violent encounters in which inmates were to fight as hard as they could.

The study found that using the gloves “increased the efficiency” of teams carrying out forced cell extractions and responding to disturbances by reducing the length of physical encounters, keeping guards from becoming exhausted and preventing injuries. They did not “significantly change” the time it took to control inmates during escorts but required less effort.

“GLOVE provides a boost in confidence to smaller or less trained members,” the study found. “Inmate compliance was immediate” compared with other methods, it added.

The electric jolt does not cause the body to freeze like a Taser shock does, but instead “works by overloading the peripheral nerve endings” of the skin to cause pain, the study said. Participants who were wet or had oil on their skin described even more powerful shocks, with one reporting discomfort for 30 minutes afterward.

ICE’s contract requires the manufacturer to deliver the gloves within six months. The company owner, Jeff Niklaus, declined to make himself available for an interview.

The White House border czar, Tom Homan, has said it could “be a while” before the gloves are in the field because ICE is still ironing out training and policy issues. A statement released on Tuesday by ICE did not address questions about the study and the status of the rollout, but said “officers are highly trained in de-escalation tactics”.

Senator Catherine Cortez Masto of Nevada said ICE had not responded to a 27 August letter in which she and 15 other Democratic Senate colleagues called for ICE to abandon its plan to buy the gloves or explain how they would be used and managed to avoid abuse. She said she still wanted answers.

“Without ICE’s responses to legitimate questions from 16 United States senators, the American public is being left in the dark about how these electric-shock gloves are being deployed and what, if any, training the agents who use them have received,” she said.