One hundred and forty minutes. That’s the amount of time between when gunmen at the Bataclan theater began rounding up survivor-hostages after their initial killing spree, and when police began their successful assault on the theater. All told, it was over 160 minutes from the first shots to when the first responders were able to reach those inside the venue: more than two and a half hours.

ISIS’s attacks in Paris offer an extreme example of a general principle of active-shooter attacks: Even the best emergency personnel cannot reach shooting victims until the threat has been neutralized. For a period of time that is very often going to be longer than it would take someone with a serious wound to bleed out, the victims are on their own.

This vulnerability is, in part, what motivates some to call for arming citizens for self-defense. But even supposing every terrorist attack was met by a civilian-led resistance, that still wouldn’t solve the problem presented by a victim shot in the thigh, dying on the floor. Whether professionals or amateurs are involved, taking down multiple shooters can take time. Active-shooter incidents present both a security and a medical challenge.

This is an entirely foreign scenario for most people, which adds an extra element of terror. But it’s also a scenario one segment of the population is uniquely familiar with: the military. And in recent years, a number of doctors have become convinced that the lessons learned in battles abroad could also be used to protect people at home: In mass shootings and terror attacks, civilians NEED to be their own first responders.

Tactical first aid for civilians,  is an adaptation of what the U.S. military calls Tactical Combat Casualty Care (TCCC)—a response to the realization that soldiers were dying on the battlefield from survivable wounds before they could make it to a hospital. A 2012 study found that almost a quarter of deaths in the wars in Iraq and Afghanistan were “potentially survivable,” and 90 percent of deaths overall occurred before the casualty could be treated at a medical center. Numbers like those, including a statistic that 90 percent of those with potentially survivable wounds died specifically from “uncontrolled blood loss,” have recently led both the military and civilian groups to focus on techniques that can be performed quickly with minimal training by non-medical personnel, in the hope that future deaths might be avoided.