The US Army last month introduced its first new lethal hand grenade since the Vietnam War, a plastic weapon that uses shock waves rather than shrapnel to kill enemies.

The new grenade, called the M111, becomes the Army’s choice for urban combat, when troops must clear indoor areas to take and hold territory, because there’s less risk of collateral damage.

It’s the first new grenade introduced for US forces since 1968, when the MK3A2 entered combat during the Vietnam War. That munition was withdrawn in the 1970s because it contains asbestos, tiny fibers of which can become lodged in the lungs leading to fatal diseases including cancer.

Its withdrawal left soldiers with the current primary grenade, the M67, which sends shrapnel in all directions when it explodes, potentially killing or injuring bystanders or friendly forces when it deflects off solid objects of metal or concrete or penetrates light walls, for example.

The use of shock waves, or blast overpressure (BOP), kills or disables enemies with the force of the explosion, vaporizing the weapon’s plastic outer shell.

Troops outside an enclosed area can throw the new grenade into that area, and enemies cannot take cover behind interior walls, furniture or appliances that shrapnel may not be able pierce, the military said.

“A grenade utilizing BOP can clear a room of enemy combatants quickly leaving nowhere to hide while ensuring the safety of friendly forces,” Col. Vince Morris, a project manager for the program at Picatinny Arsenal in New Jersey, said in an Army news release.

“When the high-pressure wave encounters someone, it violently compresses and decompresses tissue,” an Army fact sheet explains.

“The eardrums, lungs, eyes and gastrointestinal tract are most at risk of rupture and serious damage from smaller blasts.”

Larger blast waves can damage the brain or even amputate limbs, it adds.

The grenade is powered by RDX, an explosive material used extensively by the US military for decades.

The military developed the new palm-sized, cylindrical munition after experience in previous Middle East wars, Morris said in the Army statement.

“One of the key lessons learned from the door-to-door urban fighting in Iraq was the M67 grenade wasn’t always the right tool for the job. The risk of fratricide on the other side of the wall was too high,” he said.

The M67 fragmentation grenade isn’t going away. Troops will still carry it for use in open terrain “to maximize lethal fragment effects,” the statement said. They’ll just have the M111 for use indoors.

The baseball-sized M67 was introduced alongside the MK3A2 in 1968. It followed the M26, introduced in the early 1950s and the iconic Mk 2 – called the “pineapple” grenade because of its appearance – that was introduced in World War I and used through World War II and beyond.

Meanwhile, the US Marine Corps is also acquiring another BOP grenade, the M21, from Norwegian manufacturer Nammo, according to US government contracting data.

The US and other militaries have a similar weapon, a thermobaric grenade, also known as a fuel-air munition. It releases a fuel mist into the air and then ignites it, giving off a shock wave and fireball that create a vacuum effect, sucking the oxygen out of the blast area. (CNN)

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