Grenades have played a part in warfare for hundreds of years. They were originally developed around 1000 AD by the Chinese, just one application of their revolutionary gunpowder technology. Europeans came up with their own versions in the 15th and 16th centuries, with mixed results.

Photo courtesy U.S. Marine Corps, photographer Lain A. Schnaible
A U.S. Marine tosses a grenade during training exercises.
The typical design of these early grenades was a hollow metal container filled with gunpowder. Soldiers simply lit a wick and tossed the grenade -- as fast as they could. By the 18th century, these weapons had fallen out of favor: They weren't especially useful in the battle style of the time, and the simple design made them extremely dangerous.

The weapon saw a resurgence in the 20th century with the development of new modes of combat. In the trench warfare of World War I, soldiers could use grenades to take out machine gunners without ever revealing themselves to the enemy. Thanks to mechanical ignition systems that made the weapons relatively practical and safe, grenades took their place as an indispensable element in modern warfare.

Now, we'll look inside some typical grenades to find out what sets them off and see what happens when they explode. We'll also look at those invaluable elements that keep everything from exploding too early.

Grenade Basics
Broadly speaking, a grenade is just a small bomb designed for short-range use. The idea of a bomb is very simple: Combustible material is ignited to produce an explosion -- a rapid expansion of gases that produces strong outward pressure. The essential elements of a grenade, then, are combustible material and an ignition system.

What's in a Name?

Photo courtesy Department of Defense

The term grenade comes from the French term for pomegranate. In the 16th century, French soldiers (as well as other European armies) used round, pomegranate-sized bombs containing large grains of gunpowder, which resembled a pomegranate's seeds. The French army established the Grenadiers, troops trained to lob these grenades toward the enemy line.

The name "grenade" was picked up again when the weapon was reintroduced in the early 20th century. Soldiers in World Wars I and II had several other names for the weapons, however, such as pineapples, in reference to their shape and bumpy shells.

There are all sorts of combustible materials used in grenades, and they generate a range of explosion types. Some explosions will spread fire, and others will just release a lot of smoke. Some produce little more than a loud noise and a flash of
light. Some release toxic gases.

Ignition systems also vary, but they generally fall into one of two categories: time-delay igniters and impact igniters. The function of both systems is to set off the explosion after the grenade is a good distance away from the thrower. As you might expect, the igniter in an impact grenade is activated by the force of the grenade landing on the ground. With a time-delay grenade, the thrower sets off a fuze, a mechanism that ignites the grenade after a certain amount of time has passed (generally a few seconds).

One very simple impact grenade is a container filled with nitroglycerine or another material that combusts easily when jarred. In this case, the flammable liquid itself is the impact igniter. One simple but effective time-delay grenade is the Molotov cocktail, a bottle of flammable liquid with a rag sticking out of it. The rag acts as a crude fuze -- the thrower lights it and tosses the bottle. When the bottle smashes on impact, the flammable liquid flows out and is ignited by the burning rag.

The problem with both of these grenades is they can easily explode before the thrower gets rid of them. Proper grenades used by soldiers and police officers have safer, more sophisticated ignition systems, as we'll see in the following sections.

Time-Delay Grenade
The most common type of grenade on the battlefield is the time-delay fragmentation anti-personnel hand grenade. The primary function of this grenade is to kill or maim nearby enemy troops. To ensure maximum damage, the grenade is designed to launch dozens of small metal fragments in every direction when it explodes.

These sorts of grenades, which played a major role in World War I, World War II, Vietnam and many other 20th century conflicts, are designed to be durable, easy to use and easy to manufacture. The conventional design uses a simple chemical delay mechanism. The diagram below shows a typical configuration of this system, dating back to the first World War.

The outer shell of the grenade, made of serrated cast iron, holds a chemical fuze mechanism, which is surrounded by a reservoir of explosive material. The grenade has a filling hole for pouring in the explosive material.

The firing mechanism is triggered by a spring-loaded striker inside the grenade. Normally, the striker is held in place by the striker lever on top of the grenade, which is held in place by the safety pin. The soldier grips the grenade so the striker lever is pushed up against the body, pulls out the pin and then tosses the grenade. Here's what happens inside once the grenade is released:

Photo courtesy Department of Defense
The proper way to throw a hand grenade: Depress the striker lever, pull the pin, hurl the grenade.

Time-delay grenades are very effective, but they do have some significant disadvantages. One problem is their unpredictability: In some chemical fuzes, the delay time may vary from two to six seconds. But the biggest problem with time-delay grenades is that they give the enemy an opportunity to counterattack. If a soldier doesn't time a grenade toss just right, the enemy may pick it up and throw it back before it explodes.

For this reason, soldiers must use impact grenades in certain situations. An impact grenade explodes wherever it lands, so there is no chance for the enemy to throw it back. In the next section, we'll see how this sort of grenade works.

Impact Grenades
Impact grenades work like a bomb launched from an
airplane -- they explode as soon as they hit their target. Typically, soldiers don't throw impact grenades as they would a time-delay grenade. Instead, they use a grenade launcher to hurl the grenade at high speed.

U.S. ground forces typically use grenade launchers that attach to assault rifles. In one conventional gun-mounted launcher design, grenades are propelled by the gas pressure generated by firing a a blank cartridge. Some launcher grenades have their own built-in primer and propellant.

Photo courtesy U.S. Department of Defense
A soldier prepares to fire an M-203 grenade launcher mounted to an M-16 assault rifle. U.S. forces typically use rifle-attached grenade launchers like this one.

Afghan fighters and many other forces around the world use rocket-propelled grenade launchers, once mass produced by the Soviet Union. Like missiles, these grenades have a built-in rocket propulsion system.

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, 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.

The diagram below shows the elements in a simple impact grenade with a rotation arming mechanism.

The grenade has an aerodynamic design, with a nose, a tail and two flight fins. The impact trigger, at the nose of the grenade, consists of a movable, spring-mounted panel with an attached firing pin facing inward. As in the time-delay grenade, the fuze mechanism has a percussion cap and a detonator explosive that ignites the main explosive. But it does not include a chemical delay element.

Photo courtesy Department of Defense
A Kurdish refugee with a Soviet RPG-7 grenade launcher, a common weapon in smaller armies and resistance forces

When the grenade is unarmed, the fuze mechanism is positioned toward the tail end, even though it has a spring pushing it toward the nose. It is held in this position by several spring-mounted, weighted pins. The firing pin is not long enough to reach the percussion cap when the fuze is in this position. If the trigger plate is pressed in accidentally, the pin will slide back and forth in the air, and nothing will happen.

When the grenade is fired it begins to spin (like a well-thrown football). This motion is caused by the shape and position of the fins, as well as spiraled grooves inside the barrel of the grenade launcher.

The spinning motion of the grenade generates a strong centrifugal force that pushes the weighted pins outward. When they move far enough out, the pins release the fuze mechanism, and it springs forward toward the nose of the grenade. When the grenade hits the ground, the nose plate pushes in, driving the firing pin against the percussion cap. The cap explodes, igniting the detonator explosive, which ignites the main explosive.

There are dozens of variations on this idea, some with much more elaborate arming and ignition systems. But the basic principle in most of these weapons is the same.

In the future, grenade mechanisms will continue to evolve. Already, some modern grenades use an electronic fuze system instead of a mechanical or chemical fuze. In time-delay electronic grenades, the fuze consists of a digital clock and an electrically operated firing pin. When the firing button or lever is activated, the electronic system starts a precise timer. At the end of the count, the fuze mechanism releases the firing pin. Since it uses an actual clock instead of a combination of chemicals, this timing system is much more accurate than conventional fuzes.

Photo courtesy U.S. Department of Defense
This Mark 19 Mod 3 machine gun fires grenade rounds rather than ordinary bullets.

Some cutting-edge launcher-style grenades also have electronic fuzes and arming systems. The U.S. military is currently developing miniature grenades with electronic position sensors. With advanced grenade launchers, soldiers can program a grenade to explode after it has travelled a certain distance. In this way, a soldier can pinpoint particular targets, even ones behind barriers, with extremely high precision.

To learn more about grenades, including their role in military history, check out the links on the next page.

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