The Most TERRIFYING Rocket of Vietnam You’ve Never Heard Of HH

Early February 1968, Hue City, South Vietnam. Fox Company, 2nd Battalion, 5th Marines is pinned down in a courtyard trying to fight its way across the street to the Treasury building. The North Vietnamese are dug in on the roofs and in the windows, and every time a Marine lifts his head, the street lights up.

Fox Company has already paid for the ground it’s standing on. Another platoon caught a burst of fire crossing the same street minutes earlier, and half a dozen Marines are down before 3rd Platoon is even brought up to retrieve them. Now it’s their turn to find a way forward, and the way forward is blocked. 3rd Platoon’s problem isn’t manpower, it’s a wall.

8 ft of masonry wrapped around the courtyard they need to cross. The Platoon has already tried its light anti-tank rockets on it. Not powerful enough. The rounds hit the wall and do nothing but chip stone. One of 2nd Lieutenant Donald House Rats men, Lance Corporal Richard Carter, is carrying something heavier.

A long open tube, two sections locked together, a pistol grip in the middle. The 3.5-in rocket launcher. Carter crouches behind a moving tank, tracks it across the open ground, and as it passes the wall, fires. The round hits, the iron gate goes down, Fox Company moves through the gap Carter just opened, and Carter keeps the launcher loaded because there’s another wall after this one, and a Treasury building full of North Vietnamese soldiers waiting past that.

That weapon was never built for gates or walls or anything else standing still in a city. It was designed, tested, and standardized for exactly one job. Killing Soviet pattern tanks. And by the time Carter was was it through Hue, there were almost no tanks left in Vietnam to kill. Which raises the obvious question.

Why was a tank killer in that courtyard at all? Marines called it the 3.5 or the super bazooka. Officially, it was the rocket launcher 3.5 inch M20. Every part of it had been engineered around one target. Armor. Specifically, the T-34 pattern tanks that had outgrown the older 2.36 inch bazooka. A tank killer in a war with almost no tanks left in it should have been one of the first weapons quietly retired.

It wasn’t. Technical manuals kept getting published for it. It stayed in the supply system. And at Hue, an entire battalion under Colonel Ernie Cheatham pulled these launchers out of storage and hauled them into the city on purpose alongside platoons like Carter’s who were already putting them to work without waiting for orders.

That’s the contradiction sitting at the center of this. A specialized anti-tank weapon, obsolete in its own war. That Marines went looking for anyway. Ask about the M-16, the M-60, the LAW. And there’s a whole library of documentaries. This weapon sits in museum cases with a placard that mentions Korea and stops there.

The answer isn’t a scandal. It’s quieter than that. The weapon was kept for a reason that had nothing to do with why it was built. The original bazooka fired a 2.36 inch rocket. And it worked well enough early in the Second World War. Then, armor got better. By the war’s closing stages and into the post-war years, Soviet pattern tank armor had outpaced what that rocket could reliably defeat.

Reliably is the key word. It’s not that the old rocket never penetrated anything. It’s that an infantryman could no longer count on it. And at infantry range, that’s the whole problem. A tank that survives the first shot gets to take the next one. The army needed a bigger rocket. Development of a 3.

5 in launcher began late in the war, but wasn’t standardized until around 1950. By which point one tank was on everyone’s mind. The T-34. Which infantry needed to be able to stop without waiting on friendly armor. In August of 1950, the army published the manual covering the new rocket launchers M20 and M20B1. That’s the moment this became official.

Then Korea happened and the weapon proved itself immediately. American and Australian forces used the M20 against T-34-85s and it worked. That’s the part everyone remembers. But Korean War accounts record something else, too. The same launcher was highly effective against bunkers and fixed positions. Dug-in North Korean strong points that rifles and grenades couldn’t touch.

Two capabilities, same tube, same rocket. Anti-tank and anti-fortification. Hold on to that because 18 years later, it’s the only thing that keeps this weapon alive. The launcher is 3.5 in caliber, built as two sections of roughly 30 in each that lock together to fire and split apart to carry. A deliberate trade-off.

An assembly step under fire in exchange for a weapon a man can actually move with. Loaded, it runs around 15 lb. Firing is electric. Pull the trigger, a battery sends current to an igniter in the rocket motor and it lights. No primer, no breach. It’s a two-man weapon by doctrine, gunner and loader. And the second man isn’t optional.

Propellant gases vent straight out the back. Which makes the weapon effectively recoilless. And makes the space behind it dangerous enough that rear sector safety isn’t a suggestion in the manual, it’s procedure. The standard round is a shaped charge heat warhead. High explosive anti-tank. The commonly quoted service figure is 11 in of armor penetration.

Conservative. Laboratory testing recorded static penetrations averaging closer to 14 to 15 in with a maximum near 15.2. A shaped charge doesn’t blast a target apart the way a demolition charge does. It collapses a metal liner into a focused jet and drives that jet through whatever’s in front of it. Armor, masonry, packed earth, the jet doesn’t check which.

Smoke, incendiary, and inert practice rockets existed, too. But the heat round is the one that decided what this weapon actually was. The cost of all that penetration was speed. The rocket left the tube at only around 340 ft per second. Slow enough to watch it fly across a street. Maximum ballistic range topped out around 1,000 yd, but the doctrinal effective range sat closer to 150 to 300 yd.

This is a short-range weapon carrying a very long-range amount of punch. Which is exactly the trade a man crouched behind a tank in a city street needs. By the time American ground troops were fighting in Vietnam in numbers, 3.5-in launchers were already in country with Marine and Army units. But mostly sitting in storage.

Armor targets were almost non-existent. And there was no reason to hump 15 lb of two-piece steel tube through the jungle on the off chance of meeting a tank. Doctrine for it existed the whole time regardless. The Army’s field manual for the weapon went through editions in 1949, ’55, ’58, and again in December of 1961.

Kept for a fight it was rarely used in. Hue made the shortage of alternatives worse than most fights. Commanders were also holding back the artillery and the tanks main guns that might ordinarily have done this work. Reluctant to level a city built around century-old palaces and pagodas. That left rifle range weapons like the 3.

5 to do a job that usually belonged to something much bigger. So it came out selectively for bunkers, for walls, for whatever had to be opened fast. By the mid-1960s, frontline doctrine was already shifting toward lighter tools. The 90-mm M67 recoilless rifle and the new disposable 66-mm M72 LAW. The same LAW that 3rd Platoon was still finding too weak for an 8-ft masonry wall in a city like Hue 2 years after it started replacing the 3.5 on paper.

Carter’s Platoon wasn’t finished with the launcher after that first gate. Pinned down again outside the Treasury itself, Carter and his assistant gunner belly crawled across open ground under fire for close to 20 minutes to reach a schoolhouse across the street. From a second-floor hallway, the two of them fired more than 100 rounds into the Treasury and the adjoining post office over roughly 2 hours.

Sighting a window, firing, reloading, sighting the next. A North Vietnamese rocket found the hallway partway through, wounding Carter’s gunner and briefly knocking Carter unconscious. He got up, got his gunner down to the aid station, then went back upstairs and kept firing. That sequence is documented in a Naval Institute Proceedings account built from interviews with Hue veterans.

A named soldier, a named platoon, a named building. It wasn’t an isolated call. The official Marine Corps history of the battle records that Colonel Cheatham brought 3.5 inch launchers into the city specifically because they hadn’t been getting much use in the open country fighting before Hue. And quotes a Marine officer crediting the weapon’s 11 inches of penetration with letting his men, in his words, pop open the walls in front of them.

The Australian War Memorial’s own collection notes back this up from outside the American chain of command entirely, describing the M20 as still in Vietnam service even as it was being phased out, and calling it very useful against fortifications. A Marine Corps University oral history catalog even lists interviews recorded in the mid-60s specifically about using the 3.5 in Vietnam.

Proof the Corps itself thought the subject worth preserving. Though the contents weren’t accessible for this research. Now the limits, because they’re real. Beyond Hue, detailed after-action reports built around the M20 are scarce. Claims that South Vietnamese forces kept using the launcher into the late ’60s come from secondary encyclopedia-style sources, not a logistics record.

And nothing found in this research, no memoir, no oral history, no captured document, describes the M20 as a weapon the other side particularly feared. Its reputation is functional, not psychological. It worked on walls. That’s what the record says about it, and no more. No honest tally exists of how many breaches in Vietnam went through a 3.

5 versus how many Marines were hurt getting one into position. What the record does show, clearly, is that in the one battle where it mattered most, it was there. It worked, and men like Carter kept using it long after they had every reason to set it down. Carter himself was wounded again later in the campaign, medevac’d back to Phu Bai, and then volunteered to return and finish the fight with the rest of Fox Company.

The end of the super bazooka in American service was procedural, not dramatic. It wasn’t banned or disgraced. It was superseded. The M67 recoilless rifle, and especially the M72 LAW, simply fit the rest of the war better. A soldier on patrol could strap two LAWs to his ruck for the weight of one loaded 3.

5 against an enemy that mostly fought from ambush and vegetation, rather than tank formations. That arithmetic, more than any single failure, is what pushed the 3.5 to the back of the supply chain. Not a defeat, just the better tool for the war that was actually being fought. And yet, it never quite got switched off. In October of 1968, the Army issued a full technical manual for the M20A1 and M20A1B1.

Maintenance and logistics documentation still being printed for a weapon already replaced on the front line. That’s what obsolescence actually looks like from the inside. Not a ceremony, not a recall. A manual still being printed, and a supply room still stocking parts for something nobody up the chain was issuing anymore.

Because somewhere down that chain, somebody still needed one. Go back to that courtyard. The gate Carter blew down wasn’t the target the Army spent years and a war’s worth of engineering to defeat. It was masonry, not armor. But a shaped charge doesn’t know the difference. It opens a hole exactly the same way, whether it’s punching through a Soviet tank or a wall in Hue.

Anti-tank and anti-fortification were never two separate capabilities. They were one capability, pointed at two different things. That’s why a launcher built to fight a tank war Vietnam mostly didn’t have survived into a city fight nobody designed it for. Not because anyone loved it, but because the physics from 1950 still worked in 1968.

Was that quiet reliability a mark of genuinely smart logistics? An army holding onto a tool because it still worked long after the war it was built for had ended? Or was it closer to luck? A weapon nobody got around to taking away that happened to still have a job when it mattered most. Every other weapon in this story got a clean story arc.

Designed for a threat, tested against it, replaced when something better came along. The 3.5 never got that tidy an ending. It just kept getting pulled out of storage by whoever needed a hole punched in something hard war after war until eventually nobody needed it enough to keep asking. The honest verdict has to stay open. We have one extensively documented battle, a scattering of supporting accounts, and long stretches of silence in between.

It doesn’t prove how much difference this weapon made across the rest of Vietnam, and no honest accounting of that exists. It proves only that when a Marine platoon needed to get through a wall, the tool that had been sitting in storage for a war nobody was fighting anymore was the one that worked. There’s another weapon from this war with that same kind of quiet undocumented survival.

Kept in service for reasons that had nothing to do with why it was designed. That one’s next. Subscribe if you want the pieces of this war that did the real work and never made the documentaries.