Everyone knows that ammunition is dangerous.
It is designed to inflict damage, usually by hitting a target
with great force, exploding, or both. When we look at the bare-bones
theory behind ammunition, we see that it revolves around energy.
When using ammunition, our objective is to throw “balls
of energy” (projectiles, missiles, and bombs) at bad
guys and hit them—hard.
To achieve this goal, we somehow have to get these balls of
energy from the factories that manufacture them to Soldiers
and other military personnel who will use them to protect and
defend their units and themselves. Unfortunately, until we
perfect ammunition teleportation technology, ammunition is
vulnerable throughout the supply system. An article in the
March–April issue of Army Logistician, “Preserving
Readiness Through Ammunition Packaging,” described the
lengths to which packaging engineers go to protect ammunition
from problems created by the transportation system and the
environment. Readers of that article may be prompted to ask: “What’s
being done to protect us from our ammunition?” After
all, energetic materials such as propellants and explosives
are not discriminating. Give ammunition a good spark, a little
fire, or a hot fragment, and most of the energy it has stored
up for the bad guys will be hurled at the good guys instead.
Artillery Charge System (MACS) containers are staged
for a fast cookoff test.
So what are the Army’s engineers and scientists doing
to keep us safe from our own ammunition? The answer is that
they are working to make ammunition insensitive. The goal
is to develop ammunition that will react in a dangerous way
we want it to and not before.
A reaction is normally most dangerous if it is a “high
order” detonation event. In “techno-speak,” this
means an event in which a chemical reaction produces high-pressure,
high-temperature shock waves that consume the explosive material
nearly instantaneously. Shock waves from high-order detonations
can travel faster than a mile a second and cause a lot of
damage. If we put these already potentially dangerous energetics
a closed container, such as a shell, an armored vehicle,
or any other tightly enclosed space or structure, we introduce
the effect of confinement to the explosive reaction. Confinement
often increases the violence of an explosion because of a
of pressure, which eventually bursts the container that encloses
it and creates what is essentially a bomb. So not only do
we have fire, heat, and a shock wave, we also have flying
Propellants and Explosives
The ideal approach to making munitions insensitive is to use
propellants and explosives that do not react unless they are
hit with a specific stimulus. Unfortunately, this is probably
the most difficult way to make explosives insensitive. We still
want munitions to pack a punch and explode on impact with a
target. This means we have to come up with new chemical mixtures
that pack similar amounts of energy but react only when we
want them to. Scientists and engineers have developed several
new materials that are powerful but hard to set off by accident.
A word of caution, though: These materials still have more
than enough stored energy to do real damage if mishandled,
no matter how insensitive they may be.
One solution to this problem is the use of melt-away panels
to protect munitions during transport. In the event of a fire,
the panels melt before the ammunition has a chance to explode,
leaving behind huge gaping holes in the container. Munitions
may react much less violently if their containers are designed
so that the munitions cannot build up pressure from confinement.
They may burn, but they are not likely to explode. However,
a container designed with insensitivity in mind still must
be able to protect the munitions and pass stringent handling
and environmental testing. This balancing act between insensitivity
and ruggedness can be tricky.
Contained munitions can build pressure so fast that common
solutions such as pressure-relief valves will not work. One
solution to this problem is the use of melt-away panels. These
panels protect munitions during transport, but, in the event
of a fire, they melt away, leaving huge gaping holes in the
container before the ammunition has a chance to explode. When
the ammunition finally explodes, the pressure has somewhere
to go; it does not turn the container into a bomb.
Several other techniques also are being tried. Most of them
offer some way to weaken the structure of the container so
that it will vent at precise spots under pressure. Ideas such
as scoring the wall of the container or weakening the welds
have been studied, but these approaches pose challenges for
quality control and manufacturability. It is difficult to develop
a container that is strong enough to pass all packaging tests
but strategically weak enough to pass all IM tests.
are engulfed in flame during the test.
All munitions acquired by the military services must be
examined to determine if they meet established IM requirements.
is true whether the munitions are developed by the services
or procured from commercial or foreign sources. This examination
normally involves a series of six tests designed to assess
the ability of munitions (typically in their shipping configuration)
to withstand shock, heat, and impact. The specific tests
are identified during a threat hazard
assessment conducted by the acquiring service. The six
tests normally include fast cookoff, slow cookoff, sympathetic
detonation, bullet-impact, fragment-impact, and shape-charge
tests. These test requirements, methods of conduct, and
criteria can be found in Military Standard (MIL–STD)–2105,
Hazard Assessment Tests, Non-nuclear Munitions, and in
various North Atlantic Treaty Organization Standardization
Both the fast and slow cookoff tests subject munitions
to the threat of elevated temperature. In the fast cookoff,
in its container is placed over a huge vat of gasoline
jet fuel that is ignited. This raises the munition’s temperature
very quickly and tests how it reacts when it is engulfed in
fire. In the slow cookoff test, the temperature is raised again
but at a much slower rate in a specially designed oven. The
munition is placed close enough to a fire for its temperature
to rise above the ignition point, but the munition is not necessarily
engulfed in flames. In both tests, the violence of the reaction,
the degree of fragmentation, and the debris throw are evaluated.
If the munition’s reaction is no worse than burning
and no hazardous fragments are projected, the munition
tests. For the purposes of IM, a hazardous fragment is
one that produces 58 foot-pounds of energy out to a distance
of 50 feet. This is calculated either with instrumentation
during the test or by collecting and analyzing post-test
A sympathetic detonation
test involves several munitions that have been placed in their
packaged configuration and
close together as they would be for transport or storage.
The object of the test is to see if the explosion of one
will cause a simultaneous, or nearly simultaneous, explosion
in the surrounding munitions. In the test, one munition
is intentionally detonated, and the rest are free to react.
If one munition’s reaction is no worse than an explosion
and the other munitions do not react, they pass this test.
MACS container is positioned for a slow cookoff test.
Below, the container is shown after a successful
test in which the munition did not explode.
Bullet- and fragment-impact tests are performed to check a
munition’s reaction to small-arms fire and impact from
high-speed fragments that may come from sources such as exploding
bombs or artillery shells. Depending on the threat-level assessment
(what the Army thinks might be fired at the particular type
of munition being tested), various rounds are fired at the
munition in its container. The projectiles vary from 5.56 millimeters
up to .50 caliber for the bullet-impact test. Both armor-piercing
and ball ammunition are used. The Department of Defense has
developed more specific criteria for the fragment-impact test,
which includes size, shape, and speed of the fragment. If the
munition’s reaction is no worse than burning and
no hazardous fragments are thrown, it passes these tests.
The final IM test is the shape-charge jet impact. A munition
is hit with a shape-charge jet to see how it reacts. If the
munition detonates, it fails this test. (A shape-charge jet
is a hollow metal cone built into a projectile. Explosives
packed around the outside of the cone detonate on impact, squashing
the cone and forcing a fine jet of metal out of the front of
All IM testing must be approved in advance by the Army
Insensitive Munitions Board. After the tests, the results
to the board for evaluation. The board has the final say
in test implementation, test procedures, and data analysis.
other words, the Army Insensitive Munitions Board is responsible
for declaring whether or not an item is “insensitive” and
ready for fielding.
The Army’s IM program has led the way in ensuring
the safety of the munitions that Soldiers, Sailors, Airmen,
Marines use to protect and defend themselves, their units,
and their country. After all, the enemy is the only one
who should ever experience the power of our ordnance.
Robert M. Forrester is an engineer in the Logistics Research
and Engineering Directorate of the Armament Research, Development,
and Engineering Center at Picatinny Arsenal, New Jersey. He
has a bachelor’s degree in mechanical engineering from
Virginia Polytechnic Institute and State University and a master’s
degree in mechanical engineering from the Stevens Institute
of Technology in New Jersey.
Kendal M. Duncan is an explosives logistics specialist in the
Logistics Research and Engineering Directorate of the Armament
Research, Development, and Engineering Center at Picatinny
Arsenal, New Jersey. He has co-chaired the Army Insensitive
Munitions (IM) Board, served as the Army representative on
the Joint Services Insensitive Munitions Technical Panel, assisted
in managing IM improvement projects for Army munitions, and
developed the Department of Defense Insensitive Munitions Handbook
and Army policies and procedures for the implementation and
management of IM within the Army.