On April 13, 1972, a North Vietnamese armored assault — unprecedented in scale at this point in the war — smashed into South Vietnamese troops in the city of An Loc. T-54 tanks busted through into the northern part of the city … as ARVN troops scrambled to mount a defense.

Luckily for the defending troops, the North Vietnamese neglected to support their tanks with infantry. It’s a truism in military tactics that tanks left alone in urban areas will die. Saigon’s soldiers, equipped with U.S.-supplied M-72 LAW rockets, easily got off shots at the tanks’ unprotected tops and rear areas from the cover of buildings and alleyways.

“The tanks rode in ‘cockily’, with turrets open and commanders in view,” according to one U.S. Air Force report on the battle. “Led to believe that the [Viet Cong] already occupied the city … [t]hey thought their mission was a ceremonial one – to go to the Provincial Chief’s residence and run up the North Vietnamese flag.”

South Vietnamese troops “in the streets quickly disposed of this myth.”

But in a more balanced fight — such as versus Soviet armored columns in a European blitzkrieg — the results would have been very different. Not only would the Soviets come with better tactics, they’d have more heavily-armored tanks. The Pentagon was painfully aware that M-72’s rockets would bounce off those tanks’ frontal shielding.

That’s why, in May 1977, the U.S. Army hired the Brunswick Corporation — a large manufacturer that started off making pool tables and bowling balls in 19th century — to design a whole new weapon. Brunswick’s California-based defense division would refine the design of a spherical rocket dubbed the Rifleman’s Assault Weapon, or RAW.

“The unique Rifleman’s Assault Weapon will provide the gunner with high explosive power in a system which is lighter than Viper (seven pounds), and with a noise level, at release, less than the M-16 [rifle] from which it is launched,” Army engineer Alfred Carpenter wrote in a 1978 article in Army Research, Development & Acquisition Magazine. “It will also be effective at ranges up to 200 meters.”

The Viper was a more traditional anti-tank rocket launcher. But despite the RAW’s apparent benefits over these more conventional weapons, the Army eventually decided not to pursue its dream of a high-explosive, rocket-propelled bowling ball.

The RAW was the result of an arms race. The Army emerged from World War II with soldiers armed with lightweight rocket launchers — like the famous M-9 bazooka — and recoilless rifles. But during the Korean War, troops quickly reported that these weapons were ill-suited to take on Soviet-supplied armor.

During that war, the Army rushed to develop a “super bazooka” and even cooked up a rapid fire, lever-action version. But as these anti-tank weapons got bigger, they got heavier. For soldiers who had to lug these rocket launchers around, the trick was designing something both powerful and lightweight.

In the early 1960s, Army weaponeers decided to go in a different direction. The new M-72 Light Anti-Tank Weapon would be small and compact. A soldier could shoot the rocket from inside a self-contained and entirely disposable launch tube. Instead of having to train gunners to handle the weapon, units would issue the new launchers freely like hand grenades.

The new rocket launchers were simple, but the M-72’s motor was unreliable and the launch tube easily broke — putting troops at risk of being harmed by misfires. Army engineers quickly replaced the rocket’s finicky motor and went back to the drawing board to improve the system again.

Still, the M-72’s simplicity won over soldiers. “Untrained personnel could read the instructional decal on the side of the launcher, prepare the weapon for firing and achieve first-round hits,” evaluators reported from Southeast Asia in 1969.

Unfortunately, the M-72 rocket’s small size ran up against newer and better defended Soviet tanks. For most of America’s war in Vietnam, their Viet Cong and its North Vietnamese enemies lacked armored formations or declined to send them into the fight.

Until An Loc. When Hanoi’s T-54 tanks blasted into the city in April 1972, South Vietnamese troops blunted the attack with their M-72s. However, the success was mostly a product of North Vietnamese inexperience — and liberal firepower from U.S. combat aircraft.

Even when working properly, the M-72 posed a hazard to friendly troops especially in urban areas. Launching the projectile produced a lot of noise, kicked up debris and blew out hot gases from the launcher’s rear exhaust port. Confined spaces made that back blast even more dangerous.

Enter the exploding, rocket-propelled bowling ball.

Two years before the Army hired Brunswick to refine the RAW, the Defense Advanced Research Projects Agency and the U.S. Navy had kicked off a demonstration program. By the end of the project, the two groups had launched some 30 spherical rockets in various tests.

Worried about house-to-house fighting in Europe in the event of a Soviet invasion and with the An Loc incident in recent memory, the Army understood it could develop a new rocket weapon that was both short range and lethal to heavily-armored tanks.

The RAW would also have a small rocket motor, so troops wouldn’t have to worry about the noise or back blast. Special vents would spin the ball in flight, making it fly in an accurate, straight line over short distances.

The Army considered redesigning the projectile to further reduce weight, improve flight and make the weapon more suitable to different tasks. By March 1979, engineers had looked at seven different configurations, including versions dimpled like a golf ball, fitted with a trip wire to snag hazards and one with a rear-mounted circular fin. The bowling ball-shaped sphere won out after wind tunnel tests.

Even better, a soldier wouldn’t need any special tools to install the RAW’s launcher on a standard M-16 rifle. The launcher’s bracket simply locked over the barrel using the existing lug for the bayonet. The shooter could fire a blank cartridge or a standard bullet to activate the rocket motor … and out the explosive ball would go.

Perhaps most importantly, the RAW only weighed six pounds, half of that high explosives — a 50 percent payload-to-weight ratio. Most other anti-tank rockets had far higher ratios, with propellant taking up most of the weight. For the RAW, engineers could conceivably fill that space with shrapnel, incendiary material, tear gas and more.

“RAW is not limited to its present size and rifle launched configuration,” Carpenter, the Army engineer, added. The Army considered giving soldiers a larger 15-pound version and bolting an even bigger launcher onto jeeps.

“With its light weight, accuracy, low signature and versatility, the Rifleman’s Assault Weapon may prove to be one of the weapons of tomorrow’s foot soldier,” Carpenter declared.

But the Army disagreed.

The Army was more interested in the longer-ranged Viper, and foresaw a future war taking place on an open battlefield. A new high-explosive, armor penetrating 40-millimeter grenade, which a grenadier could lob from the rifle-slung M-203 launcher, would fill in for the RAW.

Expected to be a more powerful M-72, the Viper would have twice the range of the RAW and be more effective against tanks. But the new rocket was a disaster.

“The M-72 … has a low probability of hitting of hitting a tank and, when it does, a low probability of disabling it,” the General Accounting Office reported in 1984. “In testing before production, Viper did not demonstrate any significant superiority over the M-72.”

To make matters worse, the new weapon had the same sort of safety problems that plagued the M-72 decades earlier. When the Army decided to buy the Viper – over the objections of Congress and the American public – the service had already sunk more than $1 billion into the project.

n 1983, after outraged lawmakers gutted the project’s funding, the ground combat branch formally canned the program and went looking for alternatives. In the end, the Army picked up a version of the Swedish AT-4, a single-shot, disposable recoilless rifle.

Brunswick kept pushing for the RAW. The U.S. Marine Corps did take a serious look at the weapon, even putting it into limited service, according to a Wikipedia entry citing a 1995-1996 edition of the authoritative Jane’s Infantry Weapons.

By the 1980s, the Marines had moved on to a larger, reusable recoilless rifle called the Shoulder-Launched Multi-Purpose Assault Weapon, or SMAW. Like the RAW, the SMAW could fire various rounds with different warheads to handle a variety of targets — but at greater range. Like the Army, the leathernecks also adopted the AT-4.

Today, both services have AT-4s. The Marines continue to use the SMAW, while the Army has added a special, single-round bunker busting version to its arsenal.

Brunswick’s deadly bowling ball rocket is an odd footnote for a company that sold the rights to the project to defense contractor L-3 more than a decade ago. The company finally shed its sporting goods division in May.

This article by Joseph Trevithick originally appeared at War is Boring in 2015.

Image: Wikimedia Commons