The XM-174: The Army's Handheld, Automatic Grenade Launcher

By Joseph Trevithick
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With this data in hand, the Army sent 10 guns and a supply of magazines to units in Vietnam. The ground combat branch encouraged soldiers to take the weapons out on foot patrols.

But successes in the laboratory didn’t translate to success in combat.

Troops quickly reported major problems with the XM-174. For one, the magazine turned out to be extremely fragile. Pieces often broke, and small dents could jam the whole system.

To fix the drum, soldiers had to completely take it apart. Dissasemble one in combat? No thanks. During three and a half months of field tests, troops threw out 75 busted magazines.

While the weapon wasn’t prohibitively heavy, it didn’t have a shoulder sling and was onerous to lug around. Soldiers could rig an M-16 sling to the XM-174, but it was still unwieldy.

The 1st Battalion, 27th Infantry Division was the only unit that participated in the Vietnam evaluation. Within two months, soldiers took the XM-174 along on fewer than one third of their missions. The 1-27 was a “leg” infantry battalion, meaning it didn’t have vehicles to help carry the load.

Far more damning, the experimental grenade launcher had a serious safety problem. Troops discovered that the safety switch could easily move into the “fire” position … on its own.

“In one instance, while a gunner was sitting on top of a [sic] personnel carrier with the weapon on his lap, the selector was brushed from SAFE to FIRE,” the evaluators in Vietnam noted. “In this instance, two rounds discharged into the road embankment.”

Thankfully, the 40-millimeter grenades didn’t explode, because they hadn’t traveled far enough—a safety feature built into the ammunition itself. But in an another freak accident, a soldier lost an eye after a shell casing hit him in the face.

While the Army was still relatively pleased with the results coming out of Vietnam, the XM-174 was clearly not suitable for individual troops. Then other problems started cropping up.

The U.S. Marine Corps and Air Force tested the launcher on armored vehicles and helicopters. Those services had similar complaints about the system. Most notably, the gun could only toss grenades out to around 400 meters. While the XM-174’s explosive rounds were deadly, traditional bullet-firing machine guns had much greater range.

Aerojet never brought back the original design’s belt-fed system to help solve the magazine problem. But to help boost range, the company developed a new variant—dubbed the XM-174E3—that shot rocket-propelled grenades.

Yet, this complicated solution was too little, too late. Another grenade launcher was on its way.

While the Army fiddled with the XM-174, the U.S. Navy developed the vehicle- and tripod-mounted Mk 19. It chucked the faster-flying 40-millimeter grenades, and was already proving its worth in Southeast Asia.

By the early 1980s, the crew-served Mk 19 became the standard fully-automatic grenade launcher across the services. In addition, the Marines today use the MGL semi-automatic grenade launcher — first developed for the South African military in the 1980s.

But as late as 1976, Aerojet was still trying to find a buyer for the XM-174. The company’s sales literature pitched the design as a nimble weapon for the individual soldier. The firm even sent out a promotional flier depicting the gun with a shoulder sling.

But despite what you might see in action movies, most armies aren’t interested in soldiers toting their own automatic grenade launchers.

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This piece first appeared in War Is Boring here

Joseph Trevithick
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