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
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.
In this edition of HowStuffWorks,
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
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
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
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
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
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
Photo courtesy Department of
Defense The proper way to
throw a hand grenade: Depress the striker lever, pull
the pin, hurl the
With the pin removed, there is nothing holding the lever
in position, which means there is nothing holding the
spring-loaded striker up. The spring throws the striker down
against the percussion cap. The impact ignites the
cap, creating a small spark.
The spark ignites a slow-burning material in the fuze.
In about four seconds, the delay material burns all the way
The end of the delay element is connected to the
detonator, a capsule filled with more combustible
material. The burning material at the end of the delay
ignites the material in the detonator, setting off an
explosion inside the grenade.
The explosion ignites the explosive material around the
sides of the grenade, creating a much larger explosion that
blows the grenade apart.
Pieces of metal from the outer casing fly outward at
great speed, imbedding in anybody and anything within range.
This sort of grenade may contain additional serrated wire or
metal pellets for increased fragmentation damage.
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
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
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
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
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.
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.