One of mankind’s most gruesome achievements in the twentieth century is the ability to destroy the entire human race several times over. The nuclear stockpile of the united states has an estimated explosive yield approximating to 9000 million tons of TNT and the soviet stockpile can, for all practical purposes, be considered equal in destructive capacity. Britain, France and China we their smaller nuclear bludgeons on the sideline and each has plans to dramatically increase their qualitative and quantitative potential. A number of the resold nuclear powers are regularly making clandestine additions to the existing arsenals. Meanwhile, under a constant threat of instantaneous total annihilation, among regular re-appraisals of response, et al) and in the fond hope of the eventual success of the various strategic arms limitation and reduction talks, life goes fitfully on.
Nuclear and the rmonuclear weapons are usually classified as strategic, theatre and tactical or battlefield weapons, but it is impossible to draw fine distinctions. Strategic weapons are those with intercontinental delivery systems with, in popular association, very large yields. Theatre nuclear forces refer to weapons systems with ranges restricted to specific areas of operations, such as between western and Eastern Europe. Tactical nuclear weapons are usually restricted to battlefield distances of a few hundred kilometres and have relatively lower yields. Nuclear artillery, comprising nuclear capable tube artillery, rockets and missiles, falls into the third category.
Small nuclear devices were developed form the comparatively large and cumbersome atomic weapons of 1945 in a remarkably short period of time. They were deployed very widely in Europe by NATO from the mid- 1950s onwards, when they seemed to provide ‘defence on the Cheap’ in the face of the over whelming superiority of conventional Warsaw pact forces. The aim was to deter a conventional attack and to force the tactical dispersion of Soviet armour. Now the Warsaw pact has caught up and produced a stalemate at the tactical nuclear level as well. However, in the event of failure of tactical nuclear weapons remains declared NATO policy today.
With Pakistan’s known nuclear capability and her acquisition of nuclear-capable guns and missiles, it is more than likely that she will be in a position to introduce into service tactical nuclear weapons by the early 1990s possible with clandestine help from her frontline state proponent. Hence, I is important that we understand the technology and the employment of nuclear artillery.
Implosion Technique : Basic Weapon Design.
To make an efficient nuclear weapon, it is necessary to create a very high rate of neutron multiplication by the instant formation of a supercritical mass with an escalating chain reaction form previously safe material. There are two chief methods of doing this. The first and best known is commonly called the gun method (not to be confused with an artillery gun). The uranium bomb dropped on Hiroshima (12 Kilotons) was based on this method. Two sub-critical pieces of Uranium – 235 are separated at opposite ends of a cylinder akin to the barrel of a gun. Neither piece is by itself large enough for a critical mass but when bought together, they form a single piece which is supercritical. One piece s generally larger than the other and is fixed in place within a case of neutron reflecting material. At the other end of the cylinder is the smaller piece, which is backed by a conventional explosive pack that is linked to a detonating circuit. Upon detonation, the circuit closes and fires a primer. The primer ignites the explosive charge which then propels the smaller uranium piece down the barrel to join and fuse with the larger piece at a Sneed of 300 to 500 meters per second. In the resulting nuclear explosion, a very large amount of energy is released within a very short period of time with well know effects.
Plutonium 239 is twice as fissionable as Uranium 235 and is a far more efficient weapon material. However, because of its higher rate of spontaneous fission, plutonium cannot be used in the gun method design of nuclear weapons. Instead, plutonium is detonated by uniformly compressing a subcritical piece to supercritical density at a speed that avoids a destructive level of premature fission. Compression is accomplished high explosives such as triamino Trinitron benzene-to generate a uniform shock wave which ‘Implodes’ the fissionable material to densities several times normal and at speeds of upto 5000 meters per second or more. This technique of producing a supercritical mass is called ‘Implosion’.
Arrangements of high explosives designed t direct a major portion of their energy in a specific direction are known as ‘Shaped charges’ and have found a wide range of uses in modern weaponry, for example, the HEAT shell, when they are designed to cause an imploding, compressing shock wave, they are often called ‘lenses’ because of their focusing effect. A highly advanced implosion device for plutonium has a football like configuration of 32 explosive lenses arranged in an interlocking natter of 20 hexagons and 12 pentagons. Simultaneous detonation of each lens is vital. This is possible only with exceptionally sophisticated timing devices. In 1986, Pakistan is reported to have tested a non nuclear device with krypton triggers obtained clandestinely. When the lenses fire, a spherically symmetrical shock wave converges on the heavy metal liner/driver and accelerates it to a velocity up to 10 Kilometres per second, or even more. On striking the light metal reflector, the driver’s momentum creates a shock wave which converges on the core, compressing it into a supercritical density.
Using a far more primitive design than the one described above, the Ngasaki bomb (20 Kilotons) was about 10 times as efficient as the Hiroshima gum type weapon in terms of yield per unit of production cost the efficiency of the implosion cost. The efficiency of the Implosion method has remained superior despite improvements in both.
While the spherical shape of an implosion device lends itself ideally to nuclear warheads for artillery rockets and missiles, it is not at all convenient for designing shells to be fired form tube artillery. Also, a football size trigger would be too large for a 155mm shall. To overcome the disadvantages of the long and thin shape of artillery shells, nuclear weapons designers have developed a high explosive trigger shaped like a rugby ball. The asymmetrical shape of the device is compensated by arranging the firing circuits such that the more distant high explosive lenses fire a fraction of a second earlier than the closer ones. However, the ruggedisation of such sophisticated timing devices to withstand the shock of discharge, presents complicated engineering problems.
The basic yield of an ordinary plutonium implosion bomb is the equivalent of 20 kilotons of TNT. By tinkering about with the sizes of the fissionable material and employing other methods to govern the efficiency of the chain reaction process, the yield can be varied form 01 to 100 kilotons. Some of these methods can be built into the bomb so that settings can be made in the field by the twist of a dial.
Enhanced Radiation (Neutron) Bombs
In thermonuclear Weapons, the heavier isotopes of hydrogen-deuterium and tritium-are fused into helium, releasing phenomenally large amounts of energy. For fusion to take place, temperatures above 100 million degrees Celsius are required to impart enough energy to the component nuclei to overcome the positive-positive repulsion between them. This is achieve by employing an implosion device as a nuclear trigger for the H-bomb. The tremendous energy released by the speed of light in the form of X-ray and gamma photons. These photons travel some 300 times faster than the expanding fission explosions explosion and are able to bring about fusion before the fusion deice is engulfed and destroyed.
The rmonuclear weapons are such ‘Cleaner’ than fission weapons of equivalent yield because neither deuterium nor tritium is radioactive. The fission trigger does necessarily produce some radioactive fallout. However, with improved techniques like refinements in the fission trigger and the elimination of uranium – 238 tamers , among many others, radioactive fallout can be considerably reduced. Attempts are being made by the major nuclear powers to produce fusion weapons which do not require a fission device as a trigger and some may have succeeded already. The methods being experimented with are the use of an intense electric current to induce the necessary temperatures, and the fast liner’ technique-combining both magnetic and inertial confinement of the fusion fuel to achieve the required compression.
Enhanced radiation (ER) neutron weapons have been specifically development an tactical battlefield weapons, fired form guns and missiles to destroy personnel inside hard military targets. Does for dose, neutrons are more dangerous to the human body although they do not travel as far as gamma rays. Neutron radiation, which lasts only about one or two seconds, can kill soldiers in hard shelters such as tanks at a greater distance than the overpressure created by the blast. An radiation decays rapidly with distance, it is only in smaller nuclear weapons that the destructive effect of radiation is greater than that the destructive effect of radiation is greater than that of blast and beat. Thus, when the target is a large AFV concentration, it is more profitable to employ ER weapons which cause minimum ‘Collateral damage’. A one Kiloton ER weapon will produce a 3000 rad dose inside tank within a circle having a radius of 1 kilometre. A10 kiloton standard weapon would be required to produce the same level of radiation. (An exposure of about 4000 rads leads to death in two to three days. Next ground zero, where the dosage would be 10 to 20 times greater, death would be instantaneous). It is for these reasons that the ERRB (enhanced radiation/reduced blast) neutron weapons have been developed.
Details of the makeup of neutron weapons are not openly known. What is known is that it is email fusion (hydrogen) bomb with a yield of around one – Kiloton. Neutron weapons are clean and have no fallout producing uranium – 230 in their driver mechanisms. The nuclear proportion has been reduced as far as possible and only constitutes a small percentage of the overall yield. Since the purpose is to maximise neutron production, the fuel probably has an outer casing layer composed of an element such as beryllium, which gives off neutrons when struck by either the helium – 4 nuclei (alpha particles) or the neutrons produced in the fusion process and thus acts as a neutron multiplier. The basic fuel in neutron weapons is almost certainly lithium – 6 tritide. Some deuterium may be mixed into the fuel (Making it deutrated lithium tritide) or may be included as a separate layer of lithium deuteride to accelerate the fusion process by its reaction with tritium. In a fission free neutron bomb, advanced conventional explosives are used to compress the core to hyper-densities of more than 10000 times the normal density. Of the total TNT equivalent with upto another 100 tons coming from the surround shell. In artillery shells the device would be a cylinder rather than a sphere. This would be less efficient but, with extremely high compression, the weapon would still be very effective.
Nuclear Artillery in Service
In the late 1950s, faced with the soviet union’s massive conventional power threatening western Europe and with the technical ability to pack a nuclear warhead into a weapon the size of an artillery shell, the United States developed and deployed a whole range of battlefield nuclear weapons to deter a conventional attack and to force the tactical dispersion of soviet armour. Now the Warsaw pact has caught up and produced a stalemate at the tactical level as well.
Guns of the caliber of 152 mm and above are capable of firing atomic projectiles. The M422,8 in (203 mm) nuclear shell carries the w.33 warhead, using enriched uranium -235 as its fissile material and has yield of upto 2 kilotons. It can be fired by the M 115 towed howitzer and the M55, M110 A1/A2 SP howitzers at ranges upto 22 kilometers . the M753 projectile, carrying the W-79 ER warhead with a yield of 0.7 kilotons, is likely to be introduced into service shortly. The 155 mm M785 nuclear shell carrying the W82 warhead uses plutonium 239 as its fissile material and has two yields one sub kiloton and the other 4 to 5 kilotons. This can be fired from the M198 towed howitzer, the M 109 A1/A2 SP howitzer and all NATO 155 mm howitzers.
The US Field Artillery’s lance Missile is a dual purpose tactical system designed for carrying either a 450 kilogramme conventional high explosive warhead or a nuclear warhead with yield options from 1 to 100 Kilotons. Lance is Lunched from the M 752 amphibious tracked vehicle which normally caries three missiles an has a range between 72 and 120 kilometres. Pershing 1A is anther mobile is US missile with a range of 160 to 835 kilometres and 60 to 400 kiloton warhead. This is being currently replaced with Pershing IT which will carry a warhead of between 1 and 10 Kilotons but have a range as much as 2415 kilometres.
The new range will make the missile a tactical as well as a theatre nuclear weapon like the soviet SS 20. These missiles are also referred to as Euro strategic. Soviet Artillery’s tactical nuclear missiles are based mainly on FROG 3 to 7 (Free Rocket over Ground). FROG 7, the newest in the series, has a range of 70 kilometres and carries a warhead of 200 kilotons. The dual purpose scud series of missile with ranges upto 450 kilometres are being replaced with SS 23, superscud. The FROG rockets are being replaced with SS 21 and SS 22 missiles with more sophisticated guidance and improved range.
NATO’s tactical nuclear stockpile in Europe includes 2250 atomic artillery shells, 180 Pershing 1A, 90 Honest John (Rockets), 97 lance and 700 Nike Hercules SAMs. France has 42 Pluton missiles with a range from 10 to 120 kilometres and a warhead of 15 or 25 kilotons. NATO’s nuclear weapons are under ‘dual –key’ control. Also, the new neutron weapons are being stockpiled only in the continental US, instead of being forward based in Europe, which makes far more tactical sense.
The general data of various nuclear artillery weapons system in service are given in a Table overhead on the opposite page.