The 1960s were a wild, unpredictable time for America and for American weapons. The swinging sixties saw the country over the moon with rocket hysteria. The Soviets had put a man in space, so President John F. Kennedy challenged the United States to put a man on the moon. The rockets kept getting bigger and bigger. Meanwhile, back on Earth, two industrious Americans were trying to make them smaller with the creation of the gyrojet.

The Gyrojet is Born!

 The Cold War was heating up in a little southeastern nation called South Vietnam. The United States was looking to replace its standard issue rifle, the workhorse M1 Garand that secured victory for the Americans in both World War II and Korea, for use in Vietnam. Robert Mainhardt and Art Biehl wanted to make a weapon that never needed to be oiled or cleaned and had no recoil, one that hit with twice as much force as a .45-caliber round while making minimal sound. 

 
It never entirely caught on the way they’d hoped. The Gyrojet did make it to Vietnam but had more than its share of problems. Instead of replacing the most iconic U.S. military standard-issue weapons, it would be most famous for appearing in spy movies. Its memory would endure as a valuable collectors’ item among firearms enthusiasts, but not because they love the Gyrojet itself—they just want to fire one of its increasingly rare rocket rounds.

 
Robert Mainhardt began his career as an engineer and intelligence specialist for the U.S. Atomic Energy Commission. Rocketry was just a hobby. He spent his time helping young students build operational scale models of rockets while he ran his company, MBAssociates, making ICBM components. When he began working on the possibilities for miniaturized rockets, the war in Vietnam hadn’t started. He was thinking of winning wars of the future. He would create a round just 1.5 inches long that would go through an enemy at four times the speed of sound. 

Engineered to Excel

 
A standard cartridge round consists of a primer, powder, and bullet, all wrapped up in a single casing. When a weapon’s firing pin strikes the primer, an explosive chemical compound, it ignites the powder and expels the bullet from the casing and through the barrel of a gun at high velocity. How high the velocity is depends on how much powder is in the round, how big the bullet is, and how long the weapon barrel might be. 
 

The Gyrojet’s action was very different. Its firing pin was fixed in place behind the round. When the trigger was pulled, a hammer pushed the bullet onto the firing pin. The tiny rocket bullet wasn’t filled with primer and powder, however. It was filled with solid-state rocket fuel, the same nitrocellulose-nitroglycerin mixture used in bazookas. The Gyrojet hammer held the round in place just long enough for thrust to build, then pushed the hammer out of its way and off toward its target. Thrust from the round sent the hammer back into place inside the weapon, cocking it for the next semi-automatic round to fire.

Technical Difficulties

 
By 1966, Mainhardt could whittle the size of the round down while increasing its velocity. After 40 feet from exiting the barrel, a Gyrojet round could hit nearly 3,060 feet per second when it hit its target, just short of the M-16’s muzzle velocity, with almost none of the noise and twice the kinetic energy of a .45 round… after 40 feet. However, a target hit before the prerequisite 40 feet had a good chance of surviving – and may not even bleed.

 
Although Gyrojet made several different and various models, including an assault rifle, derringer, and carbine, none of them caught on with the U.S. military because its low muzzle velocity made it ineffective at close range and inaccurate at long range. If the enemy were close enough to hit, the Gyrojet wouldn’t kill them. If the enemy was far enough away to feel the weapon’s terminal velocity, there was a good chance they wouldn’t get hit anyway – any change in the wind could alter the weapon’s entire trajectory.

The GyroJet in Combat

 
Some Gyrojet weapons did find their way to Vietnam. Those who used it loved that it always worked in the weather and even underwater, but that was where the love ended. Soldiers hated how the rockets fed into the receiver, and clearing a jam or reloading in the middle of a firefight was “impractical.” These troops were using a weapon that couldn’t kill anyone attacking them, and they couldn’t reload in the middle of a battle, even if the Gyrojet bullets were effective. It’s no wonder that neither the Army, Navy, or Air Force fully embraced the Gyrojet or the rocket round concept.