UXO 101 - Identification of High Explosive Anti-Tank (HEAT) Munitions

Article submitted by UXO Guest Author Rick Stauber. For more information on the UXO Guest Author program, click here.

While the identification features differ greatly between the individual items in the ordnance families, there are identification features that are common that are used in design and manufacturing of those same items.

An example can be found with ordnance that are designed to attack and defeat an armored target utilizing what is known as a "High Explosive Anti-Tank" or HEAT design.

The key technology used in the design of HEAT munitions is the use of a "Shape Charge". A Shape Charge is a cone constructed of soft metal, typically copper. High explosive are packed around the outside of the cone (opposite of how an ice cream cone works). When the explosives are initiated from the rear or base, it implodes or collapses and inverts the cone forming an extremely high velocity pressure wave along the axis of the shape charge. This pressure wave achieves a velocity in excess of 42,000ft/sec and upon impact with the target plasticizes the armor plate at the point of impact. Molten metal as the result of the extreme heat that formed along with the molten metal from the shape charge is projected into the interior of the target, igniting flammable material within the target. Additional damage is created by super-heated gases and high speed pressure wave that accompanies the penetration. Shape Charges are very effective at defeating armor targets including tanks.

Certain physical aspects relating to the physics required in the manufacturing process identifies the use of a shape charge in various items of ordnance. Those are:

1. Break in the major diameter the ogive
2. Stand-off in front of the shape charge
3. Detonation point directly to the rear of the shape charge

The sketches and images below of various HEAT munitions depict these physical features.

Modern HEAT munitions can be identified by two key identification features. The first key identification feature is a spike-like nose assembly. This spike-like assembly can be found on large variety of modern military munitions containing a shape charge including projectiles and submunitions. The spiked nose on a HEAT warhead accomplishes two functions. It establishes a stand-off to allow proper development of the shape charge jet and it provides the location for the point initiating element for the PIBD-L fuze. The point initiating element normally consists of a sensor element constructed out of quartz crystal and is commonly called a "Piezo-Electric" crystal. The crystal when stressed produces an electrical charge, which is then used to initiate/detonate a base detonating (BD) fuze. The use of piezoelectric elements insures quick and reliable functioning of fuzing systems for items of ordnance that contain HEAT warheads. PIBD-L fuze designs are commonly referred to as "PIBD - Lucky" fuzes by the EOD and UXO community. A modern HEAT submunition round with a PIBD-L fuze is shown in the image below.

The second key identification feature found on modern HEAT munitions that require stabilization is the use of either fixed or folding fins. It was discovered early on in shape charge design that the use of a spin stabilized design limits the effectiveness of the shape charge. The spinning action partially disrupts the formation of the shape charge by countering the process in which the explosive force begins to collapse the jet formed by the shape charge. The spinning action was found to disperse the jet and dissipate the explosive forces associated with the jet itself. Comparison tests conducted early on in the development of shape charges discovered that a non-rotating 105mm HEAT projectile could penetrate 13-inches of mild steel. That same projectile when subject to normal rotation associated with spin stabilization could only penetration of 7-inches of mild steel. Because of this effect, the majority of modern HEAT munitions such as artillery projectiles and rockets utilize fin stabilization.

Both older and newer HEAT munitions share the same characteristics which were described above including:

1. A break in the major diameter or ogive to allow insertion of the shape charger liner.
2. Stand-off in front of the shape charge to allow optimum distance for the development of the penetration jet.
3. Detonation point directly to the rear or base of the shape charge to allow for the detonation wave produced by the explosives to wrap around and compress the shape charger liner to form the jet.

The images below are of a 105mm HEAT projectile and a 75mm HEAT projectile.

Both projectiles shown above use a Base Detonating fuze. Another variation of HEAT projectiles use what is called a "spit-back" design. In the "spit-back" design, the munition has a Point Detonating fuze that when functioned produces a small burst of flame directed down through the projectile body to a larger detonator in the base of the projectile. This flame causes the detonator in the base to function which then functions the high explosive charge. Spit-back HEAT munitions also have that classic break at the major diameter where the ogive is located.

The U.S. is not the only country that utilized a "spit-back" design in HEAT munitions. The image below shows a German WW II projectile that uses a base detonating (BD) fuze with a spit-back design. Upon impact, the small point detonating (PD) fuze element detonates producing an explosive jet that is shot down to the detonator located at the rear of the HEAT warhead. The base detonator then detonates the main explosive charge located at the rear of the warhead. The reference to "Spit-Back" refers to the explosive jet that is formed and is projected back to the detonator.

For more information on shape charges including detailed technical design information and a history of shape charges, visit the UXOInfo.com document library and select sub topic are 4020 - Ordnance Design.

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