Artillery Question

I recently finished reading a book about the marines at Khe Sanh and I have a question some of the military dopers might be able to help with. During the seige the marines used massive amounts of various types of artillery to protect themselves, including recoiless rifles. What is a recoiless rifle? How is it different from a cannon? What are the strengths and weaknesses of this type of weapon versus a Howitzer? I hope someone can shed some light on this for me. Thanks,


Recoil is basically due to conservation of momentum. When fired, the shell and gas from the burning gunpowder go one direction. The cannon gets pushed the other direction [recoils]. The momentum [mass x velocity] of both is the same.

Recoilless means that some of the gas formed from the burning gunpowder is vented out the back of the gun. You now balance the forward momentum [shell mass x velocity + forward gas x velocity] to the rearward momentum [gun mass x velocity + rearward gas x velocity].

The rearward gas reduces the amount of recoil on the gun. This lets you mount it on smaller vehicles. Of course, the rearward gas is wasted so the range of the gun is less. [And make sure nothing is behind the gun when it is fired as the back blast is huge]

Here’s one link, with photo, of an M18 57mm Recoilless Rifle. And one for an M20 75mm version. Both of these relate to the Korean War but presumably have some bearing. Aren’t search engines wonderful things;)

IIRC, recoilless rifles are not really compareable to howitzers - they’re short-range, direct-fire weapons used as anti-tank and infantry support. They have been phased out of most modern armies and replaced by a variety of AT rockets and missiles.

Continuing what starfish said:
A recoilless rifle shoots something out the back to counter recoil. Sometimes it the explosion gases, through a venturi; some guns use lead shot. Because of this, a recoilless can handle a “hotter” load than regular artillery.

And while a howitzer is field artillery (relatively slow, high arching shell travel), a recoilless is a light antitank weapon (really, really, high velocity/ flat arc of travel). The 106mm recoilless my dad used in 'Nam had a single-shot .50 BMG barrel on top of it as an aiming device–you fire the .50 with a tracer (muzzle velocity about 2500 fps), let it get half to 2/3 of the way to the target, then squeeze off the 106mm. The 106mm round hits before the .50…

If you ask, maybe I’ll tell you 'bout the time my dad “wasted” a $100,000 recoilless round…

Thanks for the information guys. I appreciate it. My web searches only turned up pictures of the weapons with no explaination of how they worked or why they are useful.

Gunslinger, I’ll ask. How did your dad waste a $100,000 recoiless round?

Another nice feature of the recoilless is that it can be made man-portable - well, you need a strong soldier, it’s bloody heavy - and thus provide an infantry squad with some very useful firepower.

The Swedish-made 84 mm Carl Gustav in this link: is an example of a weapon like that. (The picture shows the old M2 version). Unfortunately, unlike the 106 mm fired by Gunslinger Sr., this weapon has a low muzzle velocity, making it hard to aim. It won’t penetrate a modern tank’s frontal armour, but it’ll kill most APCs, bust bunkers and do the side or track of a tank quite nicely. It can fire some extremely unpleasant antipersonnel rounds, smoke and parachute flares.

So what you get is a shell (artillerymen sometimes coquettishly claim that their guns aren’t weapons, but their shells are) with almost the same properties as an artillery shell of the same calibre. It’s delivered from a much lighter weapon, but unfortunately with considerably lower range and with a backblast that gives the position away, prevents the weapon being used in enclosed spaces and, of course, is dangerous for people standing behind the weapon.

Infantrymen are always happy when they can carry some “organic” firepower and not have to rely on supporting units. The Vietnam-era 106 mm was, IIRC, primarily jeep-mounted and its role was ultimately taken over by TOW and other missile systems. But for close-in heavy fire support, the Carl Gustav is just the ticket, even today.

A recoilless shouldn’t be confused with a rocket launcher like the WWII bazooka (though it can look like one), because it fires shells without any propulsion of their own through a rifled barrel. Well, to add to the confusion, some shells do have rocket motors to provide extra range. Generally speaking, they kick in a couple of hundred yards from the muzzle, which makes correcting for wind a complete & utter nightmare.

This, I guess, was considerably more info than anyone ever wanted. Ah well.

S. Norman - who might still be able to fire one without hurting himself, but certainly won’t hit a target more than 100 yards away.

"This, I guess, was considerably more info than anyone ever wanted. Ah well. "

This is exactly what I wanted actually. Thanks Spiny!