The HORRORS of the M40 Recoilless Rifle in Vietnam 

The HORRORS of the M40 Recoilless Rifle in Vietnam 

February 7th, 1968. Special Forces Camp Lang Vei, 5 mi west of Khe San. A sergeant named Nicholas Fragos picks up a field telephone in the observation tower and says three words that have echoed through Special Forces history ever since. Tanks in the wire. At a recoilless rifle pit on the camp’s south side, a 26-year-old Army medic named James Holt sights through a tube older than he is.

The first North Vietnamese tank he has ever seen rolls into his crosshairs. He has 20 rounds. None of them are the right ammunition for what’s about to happen. What he does in the next 10 minutes is the only confirmed American recoilless rifle versus tank engagement of the entire Vietnam War. And the gun he uses to do it was already considered obsolete the year he picked it up.

The M40 is a single-shot, breech-loaded, tripod-mounted gun that the Army called a 106-mm even though the bore is actually 105. They renamed it to keep Marines from loading the wrong shells from a previous failed weapon. The number on the side of every M40 ever built is a clerical lie that became the gun’s name forever.

 460 lb, three-man crew, one shot at a time. The cartridge case is perforated like Swiss cheese. When you pull the trigger, propellant gases vent rearward through the breech with the same force that sends the round forward. Recoil cancels itself out. A four-man crew can carry a weapon that fires a tank-killing projectile. And the price they pay is the backblast, 75 yd deep, 150 yd wide, a cone of fire, dust, gravel, and tree limbs becoming flying shrapnel anyone standing behind the gun gets killed by.

A football field of do not stand here extending behind every shot. It is 188 dB at the gunner’s ear, the loudest impulse noise weapon in the Marine inventory. Routine pre-1970 firing was conducted without hearing protection. Every M40 gunner in Vietnam came home deaf in some measurable way. To fire it, the gunner does this.

Mounted on top of the main tube is a .50-caliber spotting rifle that fires a tracer round ballistically matched to the trajectory of the main projectile. Pull the trigger button out, the spotter fires, a tracer arcs out, and a puff of white smoke marks the impact point. If on target, push the trigger button in, the main round fires.

 If you saw a puff of white smoke near you in Vietnam, you had about 3 seconds before the second shot came. 3 seconds was usually not enough. Four kinds of ammunition, all in the same tube. HEAT, high explosive anti-tank, a copper-lined shape charge that punches through 17 in of armor at 0° impact. The round Holt was about to fire at three Russian tanks.

HEP-T, high explosive plastic, a thin-walled cylinder loaded with 3 and 1/2 kg of plastic explosive. When it hits armor, the projectile skin peels away and the explosive mushrooms against the plate. The fuse fires milliseconds later. The shockwave passes through the armor and breaks off a chunk on the inside, sending it bouncing around the tank’s interior at supersonic velocity.

The men inside die without the tank being penetrated. Beehive, 6,000 of fin-stabilized steel darts packed into the projectile. With a time fuse, the gunner can set to detonate at the muzzle or downrange. The world’s biggest shotgun. Marines who recovered enemy bodies after Beehive engagements rarely talked about it on camera.

One tube, three jobs that mattered, tanks, bunkers, and human waves. Holt had the wrong one for tanks. Lang Vei held 24 Americans, 14 Vietnamese Special Forces, 161 Montagnard mercenaries, and 282 Bru CIDG fighters. Two M40 recoilless rifles, roughly 20 rounds per gun, all high explosive. No anti-tank ammunition because nobody expected to need it.

At 42 minutes after midnight, 11 to 13 PT-76 amphibious tanks of the NVA 198th Tank Battalion came rolling up Lang Troi Road with their searchlights on. Two battalions of NVA infantry behind them. The first time the North Vietnamese had used armor in the entire war. The two lead PT-76 bulled through the perimeter wire and crushed the first line of bunkers.

Sergeant First Class James William Holt, the detachment medic, 26 years old from Hot Springs, Arkansas, was at the south side M40 pit. His military occupational specialty was medical. Every man on a Special Forces A-Team was cross-trained on every weapon in the camp. Holt had drilled on the M40 the same way he had drilled on field surgery because either skill might be the one that mattered tonight.

He sighted on the lead tank. The spotter tracer arc out. White smoke puffed on the front armor. He pushed the trigger in. The main round fired. Tank dead. He sighted on the second, same procedure. White smoke then explosion. Tank dead. Staff Sergeant Peter Tiroch, the assistant intelligence sergeant, ran across fire-swept ground to Holt’s pit and started loading.

A third PT-76 came around the burning hulks of the first two and pushed deeper into the camp. Holt sighted, fired, killed it. He took a second shot at the same target to make sure. Then he ran out of high explosive rounds. Tiroch watched Holt climb out of the pit. The two of them ran for cover seconds before NVA tank fire walked back along their backblast cloud and demolished the position they had just been firing from.

The tank crews had used the rising dust from the M40’s own backblast as their target reference. The gun killed itself just slightly too late to take Holt with it. Tiroch watched Holt run toward the ammunition bunker. The official Special Forces after-action report on Lang Vei. Tiroch watched Holt run over to the ammunition bunker to look for some handheld light anti-tank weapons.

 It was the last time Holt was ever seen. Senator John Boozman of Arkansas on the floor of the Senate 47 years later. He took charge of a silent recoilless rifle and brought it to life, destroying three enemy tanks before running out of ammunition. Master Sergeant Holt then supplied himself with light anti-tank weapons and charged into the face of the enemy, single-handedly attacking the tank formation.

The second M40 was overrun shortly after. Most of the camp’s 100 LAW rockets misfired or were duds. Nobody had briefed the Special Forces that the M72 had a 33-ft minimum arming distance. By 3:00 in the morning, the operations bunker was the only American position still holding. 5 mi east at Khe San, the Marine commander refused to launch the relief force the camp had been promised.

Of the 24 Americans at Lang Vei, 21 came home with decorations, one Medal of Honor, one Distinguished Service Cross, 19 Silver Stars. The journalist William Phillips later titled his book about the battle night of the Silver Stars. Holt was not among the bodies recovered. He was carried as missing in action for 47 years.

 We’ll come back to him. Lang Vei was the only time the M40 killed tanks. It was not the only time the M40 changed a battle. 3 weeks later in the city of Hue, the same weapon broke walls that had stood for 700 years. The M50 Ontos, six M40 tubes on a 9-ton tracked chassis, outperformed the Marine Corps’s M48 Patton tanks at Hue for one specific reason.

Tank 90-mm HE rounds didn’t have concrete-piercing fuses yet. They bounced off the citadel’s masonry. The M40’s HEAT rounds punched straight through. Lieutenant Colonel Ernie Cheatham, commanding Second Battalion, Fifth Marines, was a former defensive tackle for the Pittsburgh Steelers and the Baltimore Colts.

He earned the Navy Cross at Hue. The citation specifically names his employment of the M40. Captain Dale Dye, then a Marine combat correspondent attached to 2/5, watched Cheatham’s most famous engagement from cover. Lieutenant Colonel Cheatham ground-guided an Ontos right up to the riverbank and pointed at a spot on the citadel walls that was hitting his Marines with flanking fire from across the river.

There was some fiddling for position, then two spotter rounds, followed by ripple fire from a pair of 106s. A large chunk of wall fell into the moat surrounding the citadel, and harassing fire from that direction ceased permanently. A chunk of Imperial wall in the moat, 700 years old. Gone in two shots and a ripple.

The public health building, the treasury, where the walls were so thick the first heat rounds failed, and the Marines had to blow holes in adjacent courtyards instead. The Joan of Arc Church, the province HQ, the Dong Ba Tower. Every block of the citadel that wasn’t formally protected by the rules of engagement, Colonel Stanley Hughes, commanding the First Marines, summed up the entire Hue operation in one sentence.

The Ontos was the most effective of all Marine supporting arms. But the M40 had one weakness in the city, and it cost lives. After one engagement, Marines reportedly found two intact Ontos with empty 106 tubes and the entire crews dead beside them. They had been ordered to travel without rounds loaded, meaning the loaders had to dismount under fire to chamber the next round.

 They never made it back inside the vehicle. The story is told by Marines who were there. Official records do not confirm it, but the Ontos crews who survived Hue tell the story the same way every time. Captain Dale Dye remembered one anonymous loader he watched at Hue, a skinny little PFC from Kansas who would bolt out of his cubby in the back of the vehicle, ignoring incoming rounds pinging off the armor, calmly reload one or more of the recoilless rifles his crewmates had just discharged, and grin all the time like some carny running the

grift on rubes at a low-rent county fair shooting gallery. By the end of the battle, half of Hue was destroyed. The M40 didn’t do that alone, but it did most of the work the tanks couldn’t. At Khe Sanh, the M40 spent the entire siege getting ready for a battle that never came. Captain William Dabney commanded India Company on Hill 881 South, the highest of the hill outposts and the keystone of the entire defensive perimeter.

He had two M40s. He used them every day. His Silver Star citation for January 20th, 1968, the patrol that triggered the siege itself, includes the explicit phrase, “Directed accurate 106 mm recoilless rifle fire, which destroyed two hostile emplacements.” Seven Marines killed, 103 NVA killed. He later received the Navy Cross for the entire 88-day defense of the hill.

He was Chesty Puller’s son-in-law. But the real M40 story at Khe Sanh wasn’t about Dabney’s hill. The Khe Sanh combat base perimeter mounted 92 M40s, single guns and Ontos vehicles together, by late January 1968. Robert Pisor, in The End of the Line, wrote that the Ontos at Khe Sanh had enough flechette ammunition to pin the entire North Vietnamese Army to the face of Co Roc Mountain.

6,000 darts per round, hundreds of rounds. A wall of steel waiting for a wave that never broke against it. The doctrinal scenario the beehive was designed for, a coherent human wave assault that lasted long enough for a slow-firing recoilless rifle to engage, was rarer than commanders feared. When it did happen on Hill 881 South in 1967, the Marines on the hill watched 200 NVA forming up to attack and fired over 100 rounds of recoilless rifle fire to break up the assault.

The wave broke before it reached the wire. The flechettes meant for the main siege stayed in their crates. 77 days of waiting. The Marines who carried those rounds up the hills carried them back down without firing a single one. That is the M40 in one sentence. The weapon was always loaded, always pointed at the wire, and almost never used the way the manual described.

When it was, at Lang Vei, at Hue, on 881 South, it worked. The rest of the time it was insurance, insurance the Marines were grateful to have. The M40 was officially obsolete in 1970. The Army replaced it with the TOW missile, three times the range, better accuracy, higher hit probability against moving targets.

The Marines kept the M40s anyway. A TOW missile costs more than $10,000. A 106 mm heat round costs a fraction of that, and anti-tank platoons in Vietnam mostly weren’t shooting tanks. They were shooting bunkers, machine gun positions, walls. For that work, the M40 still earned its weight. It is in service today in Iran, Pakistan, Spain, South Korea, Brazil, and over a dozen other militaries.

Iran builds copies. The Houthis fire Iranian-built M40 rounds in Yemen. Some of those rounds, intercepted by US Central Command, were transferred to Ukraine in 2024. A weapon designed in 1955 to kill Soviet T-54 tanks on the North German Plain has been fired in every major war since Vietnam. It is still being fired today.

James Holt killed three Russian-built tanks with a recoilless rifle older than he was in 10 minutes in a dirt pit on the wrong side of South Vietnam with ammunition that wasn’t designed for the job. Then he ran into the dark to find better weapons. He didn’t come back. For 47 years his family had a name on a wall and a folded flag.

In 2015, the Defense POW/MIA Accounting Agency matched a set of remains to a dental record and brought him home to Arlington. He is buried under a white headstone in section 60. Three tanks, one M40. 10 minutes. That was the gun.