fragmentation. Ceramic armors can provide ballistic protection at less
weight per square foot, but high unit costs have limited their application.
Inorganic Nonmetallic Materials. Inorganic nonmetallic armor can
range from sand, dirt, and gravel, to snow. Protection of small-arms fire
offered by earth materials is available and effective, but costs of equipment
and labor present a disadvantage. When gravel is placed in layers between
two wooden panels, the impacting bullet usually shatters a piece of gravel in
its path. Small gravel lacks the effectiveness of layer gravel or crushed
rock since a bullet must be stopped by something comparable to its own mass.
For equal thicknesses, the ballistic protection offered by wet sand is about
one-half the protection of dry sand. No spalling and ricocheting occurs with
snow as armor material. Snow must be packed to be effective, with loose or
natural snow providing about one-half the protection of packed snow for
resisting small-arms fire.
Metallic Materials. The majority of armor materials currently used
are metallics. Metal armor falls into three general categories: (1) steel,
(2) aluminum, and (3) titanium.
Steel Armor. Rolled homogeneous steel armor conforming to
specification MIL-S-12560 has become the standard steel armor material, and
is used for comparison when considering the ballistic performance of other
armors. Homogeneous steel armor should be made as hard as possible for
defeating small-arms AP ammunition. However, as steel becomes harder it also
becomes more brittle and is more prone to severe fractures. This has formed
the basic guidance for improved steel armor, that is, to increase steel
Aluminum Armor. Aluminum alloys have been considered for
potential armor application due to their low weight. Aluminum alloys have
been designed for specific armor applications which were strengthened by
strain hardening to increase their resistance to fragment penetration.
However, as with metallic armor, high-strength aluminum alloys become more
brittle as the strength level increases and improved protection against AP
ammunition accompanies a reduction in resistance to fragmentation.
Titanium Armor. As with aluminum, titanium alloys offer
excellent ballistic protection against fragment type ammunition while
affording low weight compared to steel. Titanium armor, specified in MIL-T-
46077(MR), shows ballistic superiority over the majority of fragmentation and
Ballistic Hardening Option Recommendations. The determination of
the category of security required against ballistic threats is discussed in
Section 2. In general, the level of ballistic-resistant hardening required in
a facility design depends upon the type of facility and the category of the