How Rocket-Propelled Grenades Work

HowStuffWorks.com ^ | Shane Speck

[John Jorsett]

You may have heard the term rocket-propelled grenade, and you've probably seen news images of their use and the destruction they can cause, particularly if you've kept up with current world events in the Middle East. Rocket-propelled grenades are a commonly used explosive projectile weapon, used by many armies across the world. They play a major part in contemporary warfare, and are also highly used among insurgent and terrorist groups.

Photo courtesy Department of Defense Defense Visual Information Center
A British Soldier from the Queen`s Dragoon Guards prepares to fire an M-72 light anti-tank weapon (LAW) while taking part in weapons training at Abu Hydra Range during Operation Desert Shield.

But why? Why are rocket-propelled grenades (RPGs) so prevalent? Where did they come from and just how do they work? It's obvious they're more than just a normal grenade simply because they're rocket propelled, but just what does that mean? In this article, we'll investigate the origins of rocket-propelled grenades, how they're used and what makes them so common in military conflicts all over the world.

Mortars, Rockets and Grenades: A Brief History
The idea of remaining safe while attacking from a distance has been and always will be a major driving force when it comes to inventing weapons. Basic devices such as the slingshot, spear, bow and arrow and even the boomerang were all developed to make it easier to kill the enemy while remaining as far away from danger as possible.

Photo courtesy Department of Defense Defense Visual Information Center
RPG and mortar rounds. A cache of Soviet weaponry seized by U.S. military personnel during Operation Urgent Fury.

This need to attack from a distance, coupled with the invention of increasingly complex metalwork techniques, led to the invention of ever more complex devices for launching projectiles; in around 1500 AD mortars became popular as a siege weapon. A tube of metal from three to five feet in length, weighing several hundred pounds, would be placed on the ground and aimed into the air. Mortar shells would then be dropped into the tube and propelled upwards by an explosive charge. The mortar operator had relatively little control over where the shell landed, but despite this mortars increased in popularity and are still used today. A small mortar can easily be moved and operated by two people, and a small, high-quality shell can have the destructive force of a stick of dynamite: easily enough to destroy a small vehicle. The destructive power of the shells increases with size, of course - the larger the shell the greater the power - and mortars come in a range of sizes to reflect this. There is a trade-off between cost, weight and effectiveness. The mortar's usefulness as a weapon is limited by the lack of an accurate aiming mechanism and its relatively short range: Because the mortar shell has to go up before it can come down, much of its speed is dedicated to getting it far enough up into the air -- so against a ground target, it has limited reach.

Photo courtesy Department of Defense Defense Visual Information Center
Marines from 3rd Battalion, 5th Marines, 1st Marine Division, train with an AT-4 (light anti-armor weapon) simulator.

You can solve the range problem by improving the path of the projectile - a straight line from launching device to target is far more efficient. Enter the rocket: A rocket makes a sensible choice, because it can easily be launched from a tube device and is capable of travelling for at least a mile. In fact, a large rocket can travel up to twenty miles. The equipment required for such rockets is not unlike that used in launching mortars. Essentially, all that is needed is a set of tubes mounted on a platform or towed by a small vehicle. While this is useful, in this form it is way too bulky to replace the easily deployed mortar.

Combine certain elements of these two weapons and you've got the basics behind a rocket-propelled grenade. A small rocket is mounted on a tube, which is then aimed and launched. It may not travel as far as a larger rocket - only a few hundred feet - but it is more portable, can be aimed directly at the target, and will still do the same damage as a stick of dynamite upon impact.

RPG Basics
At its core, a rocket-propelled grenade can be thought of as something like a rocket and mortar hybrid. It's an explosive projectile weapon with two separate parts; the grenade and a device for launching it. In many cases the launcher can be reloaded, reducing the overall cost at the expense of increased weight. Weight is, of course, important if you have to carry the weapon to your target, but cost can also be important if your army is small and low on resources.

Photo courtesy Department of Defense Defense Visual Information Center
An Ecuadoran commando checks the back blast area before firing an M-72 light anti-armor weapon (LAW) during small unit training conducted as part of the joint Ecuadoran/U.S. exercise Blue Horizon '86.

The launcher is basically a tube that rests on the operator's shoulder. It is open at both ends, and a projectile with a small rocket engine is affixed to the front end of the tube. Firing is usually accomplished through a trigger mechanism, at which point the grenade's rocket engine is activated and a short, high-powered burst of ignited gases launches the grenade for a short distance - maybe between 500 to 1,000 feet (150 to 300 meters) depending on the target and the skill of the operator. An RPG operator should be aware of what's immediately behind him; the exhaust gases will flare out behind the device in a cloud of searing hot smoke.

Photo courtesy Department of Defense Defense Visual Information Center
An Opposition Forces Marine fires an AT-4 light anti-tank weapon during a skirmish.

The projectile itself travels toward the target, usually exploding upon impact. However, some modern grenades use an electronic fuze system instead of a mechanical or chemical fuze so that the projectile will detonate after a particular time-span has elapsed.

Photo courtesy Department of Defense Defense Visual Information Center
A round from an M-72 light anti-tank weapon (LAW) destroys a target at Abu Hydra Range as Marines from 7th Platoon, 1st Force Reconnaissance Company, and British soldiers from the Queen's Dragoon Guards conduct weapons training during Operation Desert Shield.

Most RPGs follow this basic operational design, although different models feature various refinements and modifications. Some are designed to be most effective against troops; some are designed to work well against armored vehicles and tanks, launching high explosive anti-tank projectiles. The M-72 Light Anti-tank Weapon (M-72 LAW) is popular with American forces, and features a pre-packaged rocket which is fired and then discarded. The M136 AT-4 also features a disposable launch device, and its 820 feet (250 meter) range and re-usable night-sight bracket has led to it becoming the U.S. Army's principal light anti-tank weapon.

M136 AT-4 Light Anti-armor Weapon

Launcher:

• Length - 40 inches (1,020 mm)
• Weight (entire system) - 14.8 pounds (6.7 kg)

  Rocket:
  

• Caliber - 3.3 inches (84 mm)
• Muzzle Velocity - 950 feet per second (290 mps)
• Length - 18 inches (460 mm)
• Weight - 4 pounds (1.8 kg)
• Maximum Effective Range - 985 feet (300 meters)
• Penetration - 15.8 inches (400 mm) of rolled homogenous armor

Source: GlobalSecurity.org

Although not favored by the U.S. Army, by far the most common rocket-propelled grenade in use today is the RPG-7, a Russian designed weapon closely related to the German Panzerfaust anti-tank weapon, dating from World War II. Like missiles, these grenades have a built-in rocket propulsion system. Let's take a closer look at the RPG-7.

Photo courtesy Department of Defense Defense Visual Information Center
Iraqi RPG-7 Rocket Propelled Grenades are among the caches of weapons found by US Marine Corps (USMC) personnel assigned to E/Company, 24th Marine Expeditionary Unit (MEU), Special Operations Capable (SOC), in the town of Qalat Sukkar, Iraq, during Operation IRAQI FREEDOM.

The RPG-7
The RPG-7 anti-tank grenade launcher is robust, simple and lethal. It is also extremely popular. As it exists today, the RPG-7 is the result of many years of revisions and modifications. The "original" RPG -- based on the German Panzerfaust anti-tank weapon - was eventually followed by the RPG-2, the RPG-3 and so on. In fact, although the RPG-4 had passed field trials in 1961, test findings of a newer model, the RPG-7, were released that same year, but with much improved firing range and armor piercing capabilities. So in 1961 it was the RPG-7, not the RPG-4, which the Soviet Armed forces adopted for actual use. Today, the RPG-7 is used by the armies of over forty different countries and is also used, reportedly, by a range of terrorist organizations in the Middle East and Latin Americas.

Now that we know what an RPG-7 is, let's take a look at how one operates.

Firing an RPG-7
The RPG operator or an artillary assistant takes a propelling charge (booster, in image below) and screws it onto the end of a warhead. Basically, this is a stabilizing pipe that has four stabilizing fins that are folded around it with two additional fins at its rear end. A cardboard container encases the back end of the stabilizing pipe. Inside the cardboard container, a squib of nitroglycerin powder is wrapped around the stabilizing pipe and a primer or charge of gunpowder is stuffed into the end of the stabilizing pipe.

The RPG operator or artillary person then takes this assembled artillery and loads it into the front end of the RPG launcher so that it lines up with the trigger mechanism.

After the RPG operator pulls the trigger, this is what happens:

• A percussion cap ignites the primer, gases build up inside the launcher’s chamber, thereby breaking apart the cardboard container and propelling the grenade forward through the barrel of the launcher. In this way, the cardboard container is a lot like the casing containing the gunpowder on a bullet.
  
  

• The force of the built-up gases throws the grenade out of the tube at approximately 384 feet per second (117 meters per second). The abrupt acceleration of the grenade leaving the launcher triggers a piezoelectric fuze that ignites the primer (pyro-retarding gunpowder mixture). This then ignites the squib of nitro, thereby activating the rocket propulsion system (sustainer motor) to carry the grenade the rest of its trajectory.

• As the grenade leaves the launcher, the fins along the stabilizing pipe spread out, which, along with the rocket motor, allow the grenade to travel a long distance at a potential speed of about 965 feet per second (294 meters per second). The grenade moves like a football, rotating through the air; the fins stabilize its flight.
  
  

• A socket in the breach block alleviates recoil during firing. The exhaust gases exit to the rear of the launcher unit and the operator is free to immediately reload the weapon. In practice, however, no RPG operator would ever remain stationary and spend the time to reload; the launching flash and whitish blue-gray smoke provides a clear indication to the enemy of the RPG launcher's location. An effective, surviving RPG operator is one who quickly changes position and gets under cover.

There are several types of grenades that can be used in the RPG-7. Some have a point initiating, base-detonating (PIBD) piezoelectric fuze: meaning that they are impact grenades. And, many others have back-up time delay systems, so that if they have not reached a target in a certain amount of time (something like four and a half seconds) the grenade will self destruct. The most commonly launched grenades are a High Explosive(HE) or High Explosive Anti Tank (HEAT) rounds.

Impact grenades must be unarmed until they are actually fired because any accidental contact might set them off. Since they are usually shot from a launcher, they must have an automatic arming system. In some designs, like the one we describe above, the arming system is triggered by the propellant explosion that drives the grenade out of the launcher. In other designs, the grenade's acceleration or rotation during its flight arms the detonator.

As for the back-up timed delay, the same fuze mechanism that sets off the the rocket would set this off. The spark ignites a slow-burning material in the fuze. In about four seconds, the delay material burns all the way through. The end of the delay element is connected to the detonator. The burning material at the end of the delay ignites the material in the detonator, thereby exploding the warhead.

Inside a grenade AND your grill...Certain crystalline materials (like quartz, Rochelle salt and some ceramics) have piezoelectric behavior. When you apply pressure to them, you get a charge separation within the crystal and a voltage across the crystal that is sometimes extremely high. It turns out one of your household appliances uses similar technology: In a grill starter, the popping noise you hear is a little spring-loaded hammer hitting a crystal and generating thousands of volts across the faces of the crystal. A voltage this high is identical to the voltage that drives a spark plug in a gasoline engine. The crystal's voltage generates a spark large enough to light the gas in the grill. This same kind of technology can be used to detonate grenades and warheads.

Tactics: How Are RPGs Used?
The basic principle behind the effective use of rocket-propelled grenades is to get as close as possible to the target and to ensure the shot is accurate. The tell-tale trail of smoke emanating from the RPG means that the RPG operator and his assistant can quickly become visible.

Buildings, vehicles with little or no armor and, of course, human beings are all vulnerable to RPG fire. In particular, the fragments from exploding grenades can cause considerable damage to troops, and this principle was used effectively against Mujahideen firing positions dug into mountain slopes. A rocket-propelled grenade would be fired above and behind the firing position, raining down shrapnel and rock onto the hidden troops.

Photo courtesy Department of Defense Defense Visual Information Center
Capt. Jose R. Atencia, 77th Explosive Ordnance Disposal Unit, handles abandoned Iraqi RPG-7 High Explosive Anti-Tank (HEAT) rockets in the aftermath of Operation Desert Storm.

Of course, rocket-propelled grenades are most efficient when deployed in small groups. Two or three shots at a vehicle from close range increases the chances of destroying the vehicle, and can even be effective in destroying an armored tank. A first shot takes out the driver's viewing prism, and further shots work their way through the armor, concentrating on one particular spot.

Helicopters, too, are easily ambushed when landing or hovering; rocket-propelled grenades downed both US Black hawk helicopters lost in Mogadishu and Somalia.

Photo courtesy Department of Defense Defense Visual Information Center
Staff Sgt. James Bradsher demonstrates the use of a Soviet-made RPG-7 portable rocket launcher during exercise Volant Scorpion.

Given the effectiveness of well-used RPGs, what strategies are there for defense? When it comes to avoiding vehicle losses from rocket-propelled grenades, a tactic adopted by less well-equipped armies is to send in infantry screens. Armies with more resources may use bombs or napalm to sweep areas in which RPGs may be located.

Another obvious tactic adopted by the Russians when fighting against the Mujahideen between 1979 and 1989 was to remain at least 1,000 feet (300 meters) away from the enemy, out of RPG-7 and AK-47 Kalashinikov assault rifle range.

RPGs: The Future

Photo courtesy Department of Defense Defense Visual Information Center
A grenade is inserted into the muzzle of a Soviet RPG-7 portable rocket launcher.

Although over forty years have passed since the 1961 introduction of the RPG, the rocket-propelled grenade remains one of the most common and effective infantry weapons currently in use. Rugged and simple, suitable for downing helicopters, disabling tanks or attacking buildings at close range, in the hands of a skilled operator, the RPG is a lethal and versatile weapon that will remain popular for some time.

Despite this, there is always room for modification. Lighter weapons with greater range and destructive capability are always being developed, and there may even be the possibility of automatic or semi-automatic rocket-propelled grenade systems.

The accuracy of rocket-propelled grenades is another area where improvements can be made. Laser guidance systems, though expensive, would greatly increase accuracy. An encoded laser could be trained on the target -- providing reference information to the rocket, thereby allowing it to make appropriate in-flight corrections to its trajectory. Other systems, perhaps utilizing GPS satellite technology could also become incorporated in future versions of RPG weaponry.

For more information on rocket-propelled grenades and related topics, check out the links on the next page.

[Squantos]

I had the hard work pleasure of destroying 250 cases (16 each case) of old Mk Duce frags once......had to cut the steel bands, open every single case, box and cardboard can and place the frags in a demolition pit on our EOD range.....yeah we tossed a few till our arms hurt for fun but the 3000 pound limit on our range made for a nice shot.

Rule to remember.... if you can see the frag the frag can see you.....:o)

[John Jorsett]

Tossed as in activating the round and throwing it by hand to explode nearby? Like that scene in Saving Private Ryan? That would be ... dramatic.

[Squantos]

Yeah we kept a few cases out after the demo shot and let the new guys function em as designed......we "tossed" em into our prior demolition shot craters around the range. All fun......suprising that there were no duds . The Mk 2 was a good tool if being stored all those decades and in two random cases we kept back didn't have a misfire. Says alot about the quality of simple designs and good workmanship and construction.


Such as the the Mk II and the RPG 7 series tools ..... solid choices for the small team tactics IMO.


Stay safe !

[Squantos]

BTW.......I think your describing the scene where they used the mortar rounds by pulling the fuze pins smacking em on a hard surface for setback and lobbing em over the rubble mound scene aren't ya ? All they had were rounds vs the rounds and the tubes.

Not frags ....mortars as I remember the scene.

[SAJ]

Aha! Another devotee of the Department of Redundancy Department!

[Calvin Locke]

I'm confused. I thought shaped charges lost efficacy when rotating. Hence smooth-bore cannons.

Is this feature a trade-off for accuracy on an RPG?

[dzzrtrock]

What puzzles me is why we spend a $1 billion to build 1 atomic-powered mouse trap instead of building a billion $1, spring-powered mouse traps. We are capturing thousands of these things from the tangos and blowing them up on an EOD range then shooting $15k rockets at the tangos. Why not just dispose of these by returning them to the tangoes in the finest point-and-shoot manner, carefully and lovingly delivered into the first mosque/school/hospital/whatever that fires on our troops? So, Abdul Mohammed Mohumud Abullah Finkelstein (III), you like RPG's? Here's one for you...and another...and another...etc....and about 1,000 rounds of 7.62mm Warsaw pact ammo, freely dispensed from a slew of captured AK-47s....(we fired our cannons 'til the barrels melted down and we grabbed an alligator and we fought another round...)

[Lurker]

I still say our guys need an updated flamethrower.

Roasting a few jihadis where they stand would have a powerful psychological impact on their buddies.

L

[Squantos]

Here's a flash fer ya ..........;o)

http://www.inetres.com/gp/military/infantry/flame/M202.html

Stay safe !

[John Jorsett]

I think your describing the scene where they used the mortar rounds by pulling the fuze pins smacking em on a hard surface for setback and lobbing em over the rubble mound scene aren't ya ? All they had were rounds vs the rounds and the tubes.

Not frags ....mortars as I remember the scene.

Yes, that's the one. I know they didn't have anything like RPGs back then, but the concept of tossing what was intended to be launched made the connection in my mind.

[Lurker]

I remember those things. We fired a few at Pendleton during AIT, but that's the last time I ever saw them.

I wonder if they're actually being issued.

L

[Squantos]

What was most impressive for me was the hand signals the rangers used then and now and was highlighted in that movied between Hanks and his sniper in the church bell tower,.....not many folks have seen that used in war movies.

Stay safe !

[Chode]

do they have a shot trap or do they need blanks to work???

[Squantos]

Archy may know of recent issues......But in all my years of active duty I saw em in training a few times but never saw em carried in SE/SW asia, Grenada, Beruit or Panama arenas.......I've never even seen a ammo dump with those stored.

Not sure of their effect and or load out these days. Last time I saw one was in a Awhuld movie where Tommy Chongs little girl Rae (finda) Dong Chong fired one from a caddy convertable.

Stay safe !

[blackeagle]

bump

[Lurker]

I'd love to see a few of those suckers being lit off on Fox News some night.

Crispy Jihadi anyone?

L

[Casloy]

Great post, learned a lot. Particularly valuable to someone in Iraq.

[ozzymandus]

It all started with the Panzerfaust. I always thought "rocket propelled grenade" was a misnomer, as tbe warhead of an anti-tank rocket has a lot more power than an ordinary hand grenade.

[wolficatZ]

 

    RPG's have been the bane of the US military for a long time now...   (Popular Mechanics, Aug '68)