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WARHEADS
13.1 OBJECTIVES AND INTRODUCTION
Objectives
1. Know the functional parts of the basic warhead package.
2. Understand the high-explosive train and the mechanics of detonation.
3. Understand the following terms as they relate to warheads: damage volume, attenuation, and propagation.
4. Understand the principles of operation of blast warheads, both air and underwater, including Mach wave and surface cutoff.
5. Understand the principles of operation of fragmentation warheads to include fragment velocity and flight.
6. Understand the principle of operation of shaped-charge and continuous-rod warheads.
7. Be acquainted with special-purpose warheads.
8. Be able to calculate fragment velocity and velocity decay versus distance.
Introduction
The basic function of any weapon is to deliver a destructive force on an enemy target. Targets of today include military bases, factories, bridges, ships, tanks, missile launching sites, artillery emplacements, fortifications, and troop concentrations. Since each type of target presents a different physical destruction problem, a variety of general and special-purpose warheads are required, within the bounds of cost and logistical availability, so that each target may be attacked with maximum effectiveness.
The basic warhead consists of three functional parts:
(1) Fuze (including the safety and arming devices)
(2) Explosive fill
(3) Warhead case
This chapter will address conventional (non-nuclear) warhead characteristics.
13.2 THE HIGH-EXPLOSIVE TRAIN
As discussed previously, high explosives comprise one category of chemical explosives. This category is subdivided into primary and secondary explosives. Recall that primary explosives are considerably more sensitive than secondary explosives. The high-explosive train is usually composed of a detonator, booster, and main charge as shown in figure 13-1. The detonator may be initiated electrically or by mechanical shock and may contain an explosive relay, pyrotechnic delay, etc.
Explosive sensitivity decreases from left to right in figure 13-1. The detonator sets up a detonation wave when initiated. The output of the detonator is too low powered and weak to reliably initiate a high-order detonation in the main charge (secondary explosive) unless a booster is placed between the two. Detonation of the booster results in a shock wave of sufficient strength to initiate a high-order detonation of the main explosive charge.
Explosives are characteristically unstable chemical compounds or mixtures of unstable compounds, and some explosives are formulated with inert binders to achieve variations in the explosive properties. An explosion of a high-explosive substance is characterized by a chemically reinforced shock wave (detonation wave) travelling at a high velocity. Figure 13-2 diagrams the principal elements of a detonation reaction. In this figure the detonator has initiated the booster, which has in turn initiated the main charge, with the detonation wave having traveled about two-thirds of the length of the main charge.
If the process were to be stopped momentarily, as diagramed in figure 13-2, an observer placed inside the unreacted explosive portion would be unaware of what was taking place because he is ahead of the supersonic shock wave. The detonation process, while very rapid, does occur over a finite period of time. The detonation wave is a strong shock wave with pressures as high as 385 kilobars depending on the type of explosive. Levels of shock energy this high are easily capable of breaking the relatively unstable chemical bonds of explosive compounds. Therefore, as the detonation wave passes through the unreacted explosive, atom-ic bonds within the explosive molecules are broken. There is then a rapid process of chemical recombination into different compounds, principally gases like CO2, H2O, N2, etc., that result in a heat energy release. This release causes rapid expansion of the gases, which reinforces the detonation wave and provides the energy that ultimately produces the destructive effect of a war-head.
The chemical reaction zone, the zone of chemical recombin-ation, is shown in figure 13-2 as a conical zone immediately behind the wave from which expansion of the explosion products occurs. The explosion products expand outwardly in a hot lum-inous state.
13.3 WARHEAD CHARACTERISTICS
The warhead is the primary element of the weapon; it accomplishes the desired end result--effective damage to the target. Damage to the target is directly related to three parameters:
13.3.1 Damage Volume.
The warhead may be thought of as being enclosed by an envelope that sweeps along the trajectory of the missile. The volume enclosed by this envelope defines the limit of destructive effectiveness of the payload.
13.3.2 Attenuation.
As shock and fragments leave the point of origin, a reduction in their destructive potential per unit area takes place. Attenua-tion can be likened to an expanding sphere, in which the energy available per unit area constantly decreases until it is comple-tely harmless.
13.3.3 Propagation.
This is the manner in which energy and material, emitted by the warhead at detonation, travel through the medium in which the blast occurs. When the propagation of a payload is uniform in all directions, it is called isotropic. If not, it is called non-isotropic. See figure 13-3.
13.3.4 WARHEAD TYPES.
For convenience of discussion, warheads will be classified into five major groups: blast (including air and underwater burst), fragmentation, shaped charge, continuous rod, and special-purpose.
13.4.1 Blast Warheads
A blast warhead is one that is designed to achieve target damage primarily from blast effect. When a high explosive detonates, it is converted almost instantly into a gas at very high pressure and temperature. Under the pressure of the gases thus generated, the weapon case expands and breaks into fragments. The air surrounding the casing is compressed and a shock (blast) wave is transmitted into it. Typical initial values for a high-explosive weapon are 200 kilobars of pressure (1 bar = 1 atmosphere) and 5,000 degrees celsius.
The detonation characteristics of a few high explosives are presented in table 13-1.
Table 13-1. Characteristics of Detonation
Loading Detonation Heat of Gurney
Density Rate Detonation Constant
Explosive g/cc M/S cal/gm M/S
Composition B
(60% RDX, 40% TNT) 1.68 7840 1240 2402
H-6 (45% RDX, 30% TNT,
20% A1, 5% WAX) 1.71 7191 923 2350
Octol (70% HMX, 30% TNT) 1.80 8377 1074 2560
TNT 1.56 6640 1080 2115
PBX-9404 (93% HMX, 6.5%
NITROCELLULOSE, .5%
Binder) 1.88 ---- ---- 2637
The shock wave generated by the explosion is a compression wave, in which the pressure rises from atmospheric pressure to peak overpressure in a fraction of a microsecond. It is followed by a much slower (hundredths of a second) decline to atmospheric pressure. This portion is known as the positive phase of the shock wave. The pressure continues to decline to subatmospheric pressure and then returns to normal. This portion is called the negative or suction phase. A pressure-time curve is shown in figure 13-4. The durations of these two phases are referred to as the positive and negative durations. The area under the pressure-time curve during the positive phase represents the positive impulse, and that during the negative phase, the nega- tive impulse. The result of this positive/negative pressure var- iation is a push-pull effect upon the target, which causes tar- gets with large volume to effectively explode from the internal pressure.
For a fixed-weight explosive, the peak pressure and positive impulse decrease with distance from the explosion. This is due to the attentuation of the blast wave. The rate of attenuation is proportional to the rate of expansion of the volume of gases behind the blast wave. In other words the blast pressure is in-versely proportional to the cube of the distance from the blast center (1/R3). Blast attenuation is somewhat less than this in-side, approximately 16 charge radii from blast center. It should also be noted that there will be fragmentation when the warhead casing ruptures.
13.4.1.1 Another aspect of overpressure occuring in air bursts is the phenomenon of Mach reflections, called the "Mach Effect." Figure 13-5 portrays an air burst at some unspecified distance above a reflecting surface, at five successive time intervals after detonation.
When a bomb is detonated at some distance above the ground, the reflected wave catches up to and combines with the original shock wave, called the incident wave, to form a third wave that has a nearly vertical front at ground level. This third wave is called a "Mach Wave" or "Mach Stem," and the point at which the three waves intersect is called the "Triple Point." The Mach Stem grows in height as it spreads laterally, and as the Mach Stem grows, the triple point rises, describing a curve through the air. In the Mach Stem the incident wave is reinforced by the reflected wave, and both the peak pressure and impulse are at a maximum that is considerably higher than the peak pressure and impulse of the original shock wave at the same distance from the point of explosion.
Using the phenomenon of Mach reflections, it is possible to increase considerably the radius of effectiveness of a bomb. By detonating a warhead at the proper height above the ground, the maximum radius at which a given pressure or impulse is exerted can be increased, in some cases by almost 50%, over that for the same bomb detonated at ground level. The area of effectiveness, or damage volume, may thereby be increased by as much as 100%. Currently only one conventional pure-blast warhead is in use, the Fuel Air Explosive (FAE). Of course, all nuclear warheads are blast warheads, and on most targets they would be detonated at altitude to make use of the Mach Stem effect.
13.4.1.2 Underwater Blast Warheads. The mechanism of an under-water blast presents some interesting phenomena associated with a more dense medium than air. An underwater explosion creates a cavity filled with high-pressure gas, which pushed the water out radially against the opposing external hydrostatic pressure. At the instant of explosion, a certain amount of gas is instantan-eously generated at high pressure and temperature, creating a bubble. In addition, the heat causes a certain amount of water to vaporize, adding to the volume of the bubble. This action immediately begins to force the water in contact with the blast front in an outward direction. The potential energy initially possessed by the gas bubble by virtue of its pressure is thus gradually communicated to the water in the form of kinetic ener-gy. The inertia of the water causes the bubble to overshoot the point at which its internal pressure is equal to the external pressure of the water. The bubble then becomes rarefied, and its radial motion is brought to rest. The external pressure now com-presses the rarefied bubble. Again, the equilibrium configura-tion is overshot, and since by hypothesis there has been no loss of energy, the bubble comes to rest at the same pressure and vol-ume as at the moment of explosion (in practice, of course, energy is lost by acoustical and heat radiation).
The bubble of compressed gas then expands again, and the cycle is repeated. The result is a pulsating bubble of gas slow-ly rising to the surface, with each expansion of the bubble creating shock wave. Approximately 90% of the bubble's energy is dissipated after the first expansion and contraction. This phen-omenon explains how an underwater explosion appears to be fol-lowed by other explosions. The time interval of the energy being returned to the bubble (the period of pulsations) varies with the intensity of the initial explosion.
The rapid expansion of the gas bubble formed by an explo-sion under water results in a shock wave being sent out through the water in all directions. The shock wave is similar in gener-al form to that in air, although if differs in detail. Just as in air, there is a sharp rise in overpressure at the shock front. However, in water, the peak overpressure does not fall off as rapidly with distance as it does in air. Hence, the peak values in water are much higher than those at the same distance from an equal explosion in air. The velocity of sound in water is nearly one mile per second, almost five times as great as in air. Con-sequently, the duration of the shock wave developed is shorter than in air.
The close proximity of the upper and lower boundaries between which the shock wave is forced to travel (water surface and ocean floor) causes complex shock-wave patterns to occur as a result of reflection and rarefaction. Also, in addition to the initial shock wave that results from the initial gas bubble expansion, subsequent shock waves are produced by bubble pulsation. The pulsating shock wave is of lower magnitude and of longer duration than the initial shock wave.
Another interesting phenomenon of an underwater blast is surface cutoff. At the surface, the shock wave moving through the water meets a much less dense medium--air. As a result, a reflected wave is sent back into the water, but this is a rarefaction or suction wave. At a point below the surface, the combination of the reflected suction wave with the direct incident wave produces a sharp decrease in the water shock pressure. This is surface cutoff. The variation of the shock overpressure with time after the explosion at a point underwater not too far from the surface is illustrated in figure 13-6.
After the lapse of a short interval, which is the time required for the shock wave to travel from the explosion to the given location, the overpressure rises suddenly due to the arrival of the shock front. Then, for a period of time, the pressure decreases steadily, as in air. Soon thereafter, the arrival of the reflected suction wave from the surface causes the pressure to drop sharply, even below the normal (hydrostatic) pressure of the water. This negative pressure phase is of short duration and can result in decrease in the extent of damage sustained by the target. The time interval between the arrival of the direct shock wave at a particular location (or target) in the water and that of the cutoff, signaling the arrival of the reflected wave, depends upon the depth of burst, the depth of the target, and the distance from the burst point to the target. It can generally be said that a depth bomb should be detonated at or below the target and that a target is less vulnerable near the surface.
13.4.2 Fragmentation Warheads.
The study of ballistics, the science of the motion of projec-tiles, has contributed significantly to the design of frag-mentation warheads. Specifically, terminal ballistics studies attempt to determine the laws and conditions governing the vel-ocity and distribution of fragments, the sizes and shapes that result from bursting different containers, and the damage aspects of the bursting charge fragmentation.
Approximately 30% of the energy released by the explosive detonation is used to fragment the case and impart kinetic energy to the fragments. The balance of available energy is used to create a shock front and blast effects. The fragments are pro-pelled at high velocity, and after a short distance they overtake and pass through the shock wave. The rate at which the velocity of the shock front accompanying the blast decreases is generally much greater than the decrease in velocity of fragments, which occurs due to air friction. Therefore, the advance of the shock front lags behind that of the fragments. The radius of effective fragment damage, although target dependent, thus exceeds consid-erably the radius of effective blast damage in an air burst.
Whereas the effects of an idealized blast payload are at-tenuated by a factor roughly equal to 1/R3 (R is measured from the origin), the attenuation of idealized fragmentation effects will vary as 1/R2 and 1/R, depending upon the specific design of the payload. Herein lies the principle advantage of a fragment-ation payload: it can afford a greater miss distance and still remain effective because its attenuation is less.
13.4.2.1 Fragment Velocity. The velocity of the fragments can be looked at in two parts: a) the initial velocity, and b) the velocity as a function of distance from the origin.
The initial static velocity of the fragments of a cylind-rical warhead depends primarily upon two factors:
(1) The charge -to-metal ratio, C/M, where C is the mass of explosive per unit length of projectile and M is the mass of metal per unit length of projectile.
(2) The characteristics of the explosive filler, particu-larly its brisance and strength. Expressing this quantitatively:
V0 = 2E C/M
1 + C/2M (13-1)
where the quantity " 2E" is known as the Gurney Explosive Energy Constant and is related to the potential energy of the given ex-plosive, as calculated in the military explosives chapter.
Table 13-2 illustrates the relationship between the charge-to-metal ratio and the initial velocities (V0) of the fragments, and table 13-1 lists typical Gurney Constants.
In this case cylinders of 5.1 cm internal diameter, filled with TNT, were employed. Notice that as the charge-to-metal ratio increases, the fragment velocity also increases.
The fragment velocity as a function of distance, s, is given by the equation:
Vs = Voe - CDpa A
2ms (13-2)
where CD is the drag coefficient, m is the mass, A is the cross-sectional area of the fragment, and pa is the density of the atmosphere at the detonation level. Thus, during flight through the air, the velocity of each fragment decays because of air resistance or drag. The fragment velocity decreases more rapidly with distance as the fragment weight decreases. For an assumed initial fragment velocity of 1,825 meters per second, a five-grain (.324 grams) fragment would lose half its initial velocity after traveling 11.25 meters, whereas a 500-grain (32.4 grams) fragment would travel 53.34 meters before losing half its velocity.
(cm) Ratio (c/m) Vo(M/Sec)
1.27 0.165 875
0.95 0.231 988
0.79 0.286 1158
0.48 0.500 1859
Fragment trajectories will follow paths predicted by the principles of external ballistics (Chapter 20). For determining the effectiveness of almost all fragmenting munitions, the sub-sonic trajectory of the fragments can be ignored. As a result, the density of fragments in a given direction varies inversely as the square of the distance from the weapon. The probability of a hit on some unshielded target is proportional to the exposed pro-jected area and inversely proportional to the square of the dis-tance from the weapon (1/R2). For an isotropic warhead:
P (hit) Frag Density X Area Target # Fragments X AT (13-3)
4R2
13.4.2.2 Fragment Flight. The fragments of a warhead travel outward in a nearly perpendicular direction to the surface of its casing (for a cylindrical warhead there is a 7- to 10-degree lead angle). Figure 13-7 portrays a typical fragmentation pattern. The tail and nose spray are frequently referred to separately as the "forty-five degree cone," which is an area of less dense fragmentation. If this payload were to be detonated in flight, the dense side spray would have a slight forward thrust with an increased velocity equal to missile flight velocity.
The angle of the side spray in figure 13-7 would be defined as the beam width of this fragmenting payload. Fragment beam width is defined as the angle covered by a useful density of fragments. Beam width is a function of warhead shape and the placement of the detonator(s) in the explosive charge.
The latest air target warheads are designed to emit a nar-row beam of high-velocity fragments. This type of warhead, called an annular Blast Fragmentation warhead (ABF), has a frag-mentation pattern that propagates out in the form of a ring with tremendous destructive potential. A newer type of fragmentation warhead is the Selectively Aimable Warhead (SAW). This "smart" warhead is designed to aim its fragment density at the target. This is accomplished by the fuzing system telling the warhead where the target is located and causing it to detonate so as to maximize the energy density on the target.
13.4.2.3 Fragment Material. The damage produced by a fragment with a certain velocity depends upon the mass of the fragment. It is therefore necessary to know the approximate distribution of mass for the fragments large enough to cause damage. Mass dis-tribution of payload fragments is determined by means of a static detonation in which the fragments are caught in sand pits. In naturally fragmenting payloads where no attempt to control frag-ment size and number is made, fragmentation may randomly vary from fine, dust-like particles to large pieces. Modern warheads use scored casings and precut fragments to ensure a large damage volume. See figures 13-8 and 13-9.
13.4.3 Shaped Charge Warheads
The discovery of what is variously referred to as the shaped charge effect, the hollow charge effect, the cavity effect, or the Munroe effect, dates back to the 1880s in this country. Dr. Charles Munroe, while working at the Naval Torpedo Station at Newport, Rhode Island, in the 1880s, discovered that if a block of guncotton with letters countersunk into its surface was det-onated with its lettered surface against a steel plate, the let-ters were indented into the surface of the steel. The essential features of this effect were also observed in about 1880 in both Germany and Norway, although no great use was made of it, and it was temporarily forgotten.
A shaped charge warhead consists basically of a hollow liner of metal material, usually copper or aluminum of conical, hemispherical, or other shape, backed on the convex side by explosive. A container, fuze, and detonating device are included. See figure 13-10.
When this warhead strikes a target, the fuze detonates the charge from the rear. A detonation wave sweeps forward and be-gins to collapse the metal cone liner at its apex. The collapse of the cone results in the formation and ejection of a continuous high-velocity molten jet of liner material. Velocity of the tip of the jet is on order of 8,500 meters per sec, while the trail-ing end of the jet has a velocity on the order of 1,500 meters per sec. This produces a velocity gradient that tends to stretch out or lengthen the jet. The jet is then followed by a slug that consists of about 80% of the liner mass. The slug has a velocity on the order of 600 meters per sec. This process is illustrated in figure 13-11.
When the jet strikes a target of armor plate or mild steel, pressures in the range of hundreds of kilobars are produced at the point of contact. This pressure produces stresses far above the yield strength of steel, and the target material flows like a fluid out of the path of the jet. This phenomenon is called hydrodynamic penetration. There is so much radial momentum associated with the flow that the difference in diameter between the jet and the hole it produces depends on the characteristics of the target material. A larger diameter hole will be made in mild steel than in armor plate because the density and hardness of armor plate is greater. The depth of penetration into a very thick slab of mild steel will also be greater than that into homogeneous armor.
In general, the depth of penetration depends upon five factors:
(1) Length of jet
(2) Density of the target material
(3) Hardness of target material
(4) Density of the jet
(5) Jet precision (straight vs. divergent)
The longer the jet, the greater the depth of penetration. There-fore, the greater the standoff distance (distance from target to base of cone) the better. This is true up to the point at which the jet particulates or breaks up (at 6 to 8 cone diameters from the cone base). Particulation is a result of the velocity grad-ient in the jet, which stretches it out until it breaks up.
Jet precision refers to the straightness of the jet. If the jet is formed with some oscillation or wavy motion, then depth of penetration will be reduced. This is a function of the quality of the liner and the initial detonation location accuracy.
The effectiveness of shaped charge warheads is reduced when they are caused to rotate. (Degradation begins at 10 RPS).Thus, spin-stabilized projectiles generally cannot use shaped-charge warheads.
The effectiveness of a shaped charge payload is independent of the striking velocity of the warhead. In fact, the velocity of the warhead must be taken into consideration to ensure that detonation of the payload occurs at the instant of optimum stand-off distance. The jet can then effectively penetrate the target. Damage incurred is mostly a function of the jet and material from the target armor detached off the rear face. This action of tar-get material joining with the shaped charge jet is known as spal-ling. The extent of spalling is a function of the amount of ex-plosive in the payload and the quality of the target armor. Fig- ure 13-12 illustrates the results of armor plate spalling.
13.4.4 Continuous-Rod Warheads
Early warhead experiments with short, straight, unconnected rods had shown that such rods could chop off propeller blades, engine cylinders, and wings, and in general, inflict severe damage to a fighter aircraft. However, rod warheads were ineffective against larger planes because the nature of most bomber aircraft structures permits a number of short cuts in their skin without lethal damage occurring. It was found, however, that long, continuous cuts would do considerable damage to a bomber; therefore, the continuous-rod warhead was developed.
Upon detonation, the continuous-rod payload expands rapidly into a ring pattern. The intent is to cause the connected rods, during their expansion, to strike the target and produce damage by a cutting action (see figure 13-13).
Each rod is connected end-to-end alternately and arranged in a bundle radially around the main charge. The burster is designed such that upon detonation the explosive force will be distributed evenly along the length of the continuous-rod bundle. This is important in order to ensure that each rod will maintain its configuration and consequently result in uniform integrity of the expanding circle. Figure 13-14 serves to illustrate the arrangement of the bundle on a section of the main charge, and its accordion-like appearance as the section begins expansion.
The metal density of a normal fragmentation warhead attenuates inversely with the square of the distance (1/R2). However, because it is non-isotropic, the metal density of a continuous-rod payload attenuates inversely as the distance from the point of detonation (1/R).
To ensure that the rods stay connected at detonation, the maximum initial rod velocity is limited to the range of 1,050 to 1,150 meters per second. The initial fragment velocities of fragmentation warheads are in the range of 1,800 to 2,100 meters per second. Thus, in comparison, continuous-rod warheads cannot produce as much destructive energy potential as fragmentation warheads.
13.4.5 Special-Purpose Warheads
There are other means of attacking targets than with blast, frag-mentation, shaped charge, or continuous rod payloads. Several types of payloads are more specialized in nature, designed to perform a specific function. A few of these will be described.
13.4.5.1 Thermal Warheads--The purpose of thermal warheads is to start fires. Thermal payloads may employ chemical energy to kindle fires with subsequent uncontrollable conflagrations, or nuclear energy to produce direct thermal destruction as well as subsequent fires. Thermal payloads of the chemical type may be referred to as incendiary or fire bombs. Many area targets are more effectively attacked by fire than by blast or fragmentation. Thermal warheads, principally in the form of aircraft bombs (Napalm), have been developed for use against combustible land targets where large and numerous fires will cause serious damage.
13.4.5.2 Biological and Chemical Warheads--A biological warhead uses bacteria or other biological agents for accomplishing its purposes of causing sickness or death, and is of extreme strat-egic importance since it is capable of destroying life without damaging buildings or materials. The poisoning of water supplies is probably the single most efficient way of destroying enemy personnel. The war potential of the enemy, such as guns, missile launching site, etc., are thus left intact and at the disposal of the attacker. The biological agent may be chosen so that it causes only temporary disability rather than death to enemy per-sonnel, thereby making it relatively simple to capture an enemy installation. A small explosive charge placed in a biological payload is useful in the dispersion of biological agents. A chemical warhead payload is designed to expel poisonous sub-stances and thus produce personnel casualties. Binary warheads are stored with two inert subsections. When properly fuzed, they combine to form a lethal payload.
13.4.5.3 Radiation Warheads--All nuclear weapons emit radiation. However, an enhanced radiation weapon can be designed to maximize this effect. Chapter 14 will adress this topic.
13.4.5.4 Pyrotechnic Warheads--Pyrotechnics are typically em-ployed for signaling, illuminating, or marking targets. In the simplest form they are hand-held devices. Some examples of more elaborate warhead payloads are as follows:
(a) Illumination--These warheads usually contain a flare or magnesium flare candle as the payload, which is expelled by a small charge and is parachuted to the ground. During its descent the flare is kindled. The illuminating warhead is thus of great usefulness during night attacks in pointing out enemy fortifica-tions. Illumination projectiles are used with great effective-ness in shore bombardment. Illuminating warheads are also used as aircraft flares and flare rockets to assist in the attack of the ground targets and submarines. Because these flares are difficult to extinguish if accidentally ignited, extreme caution in their handling is required.
(b) Smoke--These warheads are used primarily to screen troop movements and play a vital role in battlefield tactics. A black powder charge ignites and expels canisters that may be designed to emit white, yellow, red, green, or violet smoke.
(c) Markers--White phosphorus is commonly employed as a pay-load to mark the position of the enemy. It can be very danger-ous, especially in heavy concentrations. The material can self-ignite in air, cannot be extinguished by water, and will rekindle upon subsequent exposure to air. Body contact can produce seri-ous burns. Copper sulphate prevents its re-ignition.
13.4.5.5 Anti-Personnel Warheads--Such warheads are designed to destroy or maim personnel or to damage material enough to render it inoperable. In the area of field artillery, the flechette or beehive round is an example of an anti-personnel warhead. The payload in this projectile consists of 8,000 steel-wire, fin-stabilized darts. Upon detonation the darts, or flechettes, are sprayed radially from the point of detonation, normally within sixty feet of the ground. It is extremely effective against per-sonnel in the open or in dense foliage.
13.4.5.6 Chaff Warheads--Chaff may be employed to decoy enemy weapons or blind enemy radar. The payload typically consists of metal-coated fiberglass strands cut in lengths determined by wavelength of the RF energy to be countered. Chaff may be dispensed in a variety of warheads, including projectiles and rockets.
13.4.5.7 Cluster Bomb Units (CBU)--CBUs are air-delivered wea-pons that are canisters containing hundreds of small bomblets for use against a variety of targets, such as personnel, armored ve-hicles, or ships. Once in the air, the canisters open, spreading the bomblets out in a wide pattern. The advantage of this type of warhead is that it gives a wide area of coverage, which allows for a greater margin of error in delivery. Rockeye is a CBU that contains over 225 bomblets. APAM is an improved Rockeye type CBU that contains over 500 bomblets. Like Rockeye, each bomblet con-tains a shaped charge warhead. The APAM bomblet also has an anti-personnel/soft target detonation mode.
13.4.5.8 Mines--Mine warheads use the underwater blast princip-les described earlier to inflict damage on the target ship or submarine. The damage energy transmitted is approximately equal-ly divided between the initial shock wave and the expanding gas bubble. If the target is straddling the gas bubble, then it will have unequal support and may be broken in two. As the detonation depth increases, particularly in excess of 180 feet, the effect of the gas bubble causing damage is greatly diminished; there-fore, bottom mines are rarely used in waters exceeding 180-200 feet. Mines typically use the highest potential explosives, gen-erally 1.3 to 175 relative strength. Captor mines have also been developed that actually launch a smart torpedo that then passive-ly and actively homes in on the target before detonation.
13.4.5.9 Torpedoes--Torpedo warheads must be capable of damaging both ships and submarines. Homing in on the screws can achieve a mobility kill. Detonation under the keel at midships can cause the severe gas-bubble damage mentioned with mines, and if the depth is less than 300 feet, the reflected shock wave can sub-stantially increase the damage effects. Torpedoes that actually impact the hull of a ship or submarine have to overcome the doub-le hull/void structure. Deep-diving submarines with especially thick hulls require highly specialized warheads. Shaped charge warheads are envisioned as the solution to this problem.
13.4.5.10 Anti-tank warheads--Because of extensive innovative advances in tank armor, shaped charge warheads have grown in diameter and other types of warheads have been developed.
(a) The kinetic energy defeat mechanism employs a very heavy, hard, metal-core penetrator traveling at extremely high velocity. The penetrator is fin stabilized and uses a discarding sabot to increase its size to fit the gun barrel diameter when fired. The armor plate is thus defeated by either: (1) ductile or plastic flow failure, or (2) by shearing or plugging such as a "cookie cutter" would do. The shape of the penetrator tip on this weapon (or any other weapon) is the determining factor.
(b) The high-explosive, plastic defeat mechanism uses a high-explosive plastic filler in a shell that deforms on impact to effectively put a large glob or cone of plastic explosive against the side of the armor. The timing of the base detonator is critical for maximum effect. The armor is not actually pen-etrated, but extensive spalling is caused on the opposite side of the armor. This warhead is limited to lighter armor than the shaped-charge or armor-piercing kinetic energy warheads.
13.5 SUMMARY
High explosives are basically employed in warheads to produce damage. Initiation of the reaction is achieved through the high-explosive train. Rapidity of the reaction is enhanced by the phenomenon of detonation. The generation of heat and the evolution of gases produce pressure effects and radiation, which constitute the damage potential of the warhead.
This chapter has presented a number of ways in which these principles may be applied to produce an explosive force. Through a basic description of warheads, it may be seen how a specific target may determine the warhead characteristic to be employed in order to counter that target. Variation upon the five basic types of warheads results in more specialized designs developed to provide the military arsenal with greater flexibility.
13.6 REFERENCES/BIBLIOGRAPHY
Commander, Naval Air Systems Command, Joint Munitions Effectiveness Manual, Basic JMEM A/S. NAVAIR 00-130-AS-1. Washington, D.C.: GPO, 1974.
Commander, Naval Ordance Systems Command. Weapons Systems Fundamentals. NAVORD OP 3000, vol. 2, 1st Rev. Washington, D.C.: GPO, 1971.
Departments of the Army and Air Force. Military Explosives. Wahington, D.C., 1967.
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