Patients were transported in a system designed during the 2014 Ebola outbreak.

Three U.S. government contractors who tested positive for the novel coronavirus were evacuated out of Afghanistan on Saturday, according to Air Mobility Command.

The contractors were flown on a C-17 aircraft to Ramstein, Germany, where they’ll receive treatment at Landstuhl Regional Medical Center. Their evacuation from Afghanistan marked the first time the U.S. military has transported coronavirus-positive patients since the outbreak began.

In order to minimize the risk of contagion to the aircrew, while at the same time allowing for medical care, the Air Force used a Transport Isolation System, an infectious disease containment unit that can be secured inside the aircraft. The system was developed during the 2014 Ebola outbreak, but this is the first time it’s been used to transport patients.

The approximately 20-person crew aboard the C-17 included an infectious disease doctor, a critical care transport team, an aeromedical evacuation crew and Transport Isolation System operators.

As of Friday, 205 Department of Defense contractors were living with coronavirus, according to Pentagon data. Another 2,031 service members and 493 DOD civilian employees also had confirmed cases.

The Pentagon, citing operational security concerns, has declined to reveal the total number of service members affected in a given location.

On March 24, the NATO-led mission in Afghanistan announced that four coalition service members had tested positive for coronavirus — the first positive tests affecting the mission — but would not reveal their nationalities. At the time, approximately 1,500 service members and civilians who had either recently arrived in Afghanistan or returned from leave were isolated in “screening facilities” as a preventative measure, according to Resolute Support. Another 38 personnel were “exhibiting flu-like symptoms” and placed in isolation to receive care.

Knowing it may need to transport coronavirus patients in Europe, Africa or the Middle East, the Air Force earlier deployed two Transport Isolation Systems and their crews to Germany.

In a Pentagon briefing earlier this month, Deputy Commander of Air Mobility Command Lt. Gen. Jon Thomas called such bio-containment units “the best means to transport a COVID-positive patient.”

“While treatment of patients in place is always the preferred option, we anticipate there will likely be circumstances in which such care will not be available, and the best option will be to transport the patient to alternative facilities,” he said.

Meanwhile, medical professionals from the Air Force’s School of Aerospace Medicine are training medics at Joint Base Charleston in South Carolina to operate the system in anticipation of additional future use. Medics learn how to properly put on personal protective equipment, follow waste management procedures, simulate in-flight patient care and familiarize themselves with equipment and inventory, among other activities.

The Transport Isolation System consists of one antechamber module and two isolation modules — for a total of two patients per unit — and can be secured on C-130H, C-130J and C-17 aircraft. The antechamber module provides a space for medical personnel to safety decontaminate and remove personal protective equipment. A C-17 can hold two system units for a total of four patients.