The US Army has just unleashed a deadlier grenade designed for indoor use. Here’s how it works.

The US Army has unveiled the M111, its first new lethal hand grenade since the Vietnam era. This one ditches the classic Hollywood image of shrapnel tearing through everything in sight and replaces it with something that sounds somehow more terrifying: a shock wave designed to crush the human body from the inside.

A traditional grenade, like the M67, scatters metal fragments in all directions. This works well in open spaces, but is less ideal indoors where it can potentially create shrapnel that can bounce back at the person who threw it. The M111 eliminates the problem of shrapnel by instead vaporizing its plastic shell on detonation, leaving a blast overpressure wave that doesn’t care what’s in the way.

In the world of murder, that’s a selling point.

The US Army developed a more lethal grenade intended for indoor use

This means that in urban combat, which can take place in narrow corridors and narrow apartments, the M111 does not need line of sight. The pressure wave travels through openings, around obstacles and into bodies, violently compressing organs. Eardrum ruptures. The lungs collapse. Internal damage increases rapidly with no visible wounds. Suddenly, ducking behind cover isn’t as effective a strategy as it used to be.

According to CNN, the Army says the M111’s development learned a lot from the Iraq War, where the risk of accidentally harming friendly forces with fragmentation grenades was quite high. The new grenade is no less lethal; it’s just a more controlled mortality.

The old M67 won’t be officially retired anytime soon, as it still has its place in open terrain, where 360-degree dispersion of shrapnel is the point.