NEWS AND VIEWS Who wants a big gun, and why?

The discovery of components for a huge gun apparently being assembled in Iraq has caused a sensation, and has stimulated endless speculation about its nature. Here is some more.

COULD there be a connection between the simply goes to waste. but increasing the range from 40 km to, discovery, at London airport three weeks Apparently, the optimum ratio of say, 400 km would require that the muzzle ago, of capacitors designed for triggering barrel length to calibre is determined velocity should be increased more than nuclear explosions and the way in which empirically to be roughly constant, threefold, which is a tall order. Would that components of a huge gun bound for Iraq yielding a maximum muzzle velocity and be feasible? have come to light at British and Greek thus range, in practice roughly 600 m S·l Given the complexity of what happens ports in the past few days? Could the and 40 km respectively. (The use of under­ in a gun-barrel, there seems little future in triggering devices have been intended not sized projectiles allows the terminal attempts at precise calculation, but a little for use with nuclear explosives but, velocity to be increased, but uneconom­ handwaving may not be inappropriate. rather, to detonate explosive charges at ically.) The ideal characteristics of the The sections of steel tubing impounded by intermediate points along an overlong gun propellant naturally vary with the mass of the British authorities all have the same barrel? What follows is almost entirely the projectile. But why should Iraq be wall diameter (more than 20 cm). Assum­ speculation, but may go some way to bent on building a gun with an over-long ing, conservatively, that half the acceler­ illuminate some of the melodrama of the barrel? Even with an internal diameter of ation of the projectile is normally brought past few weeks. 1 metre, a barrel 40 m long should give the about in the first quarter of the barrel, any The circumstances are these. Ten days longest range. means of renewing the initial shock wave ago, British Customs and Excise impoun­ One explanation is that Iraq planned to one quarter of the way along would add ded four massive steel tubes at a British build a gun in which the muzzle velocity of to the terminal velocity. And so on, at port, announcing that they were sections the projectile would be increased by repeated intervals along the length. of a gun barrel. It has since come to light replenishing the supply of propellant But not pro rata. At successive inter­ that the manufacturers, in Sheffield, had gases at intervals along the length of the mediate intervals along the barrel, the made a total of 16 tubes of the same barrel. Apparently this has been tried relative velocity of the shock-waves from design, most of which had already been before in the German project, during the intermediate propellant charges would be shipped to Iraq. Initial scepticism of the Second World War, for building a gun reduced, and so would be the efficiency customs' claim has been exorcised by the capable of reaching London from the with which momentum is transferred from discovery last weekend, at the Greek port coast of the mainland. Experience seems the gases to the projectile. Again there of Patras, of what seems to be part of the to have shown that one firing in three will be a limiting muzzle velocity - the breech mechanism of a huge gun, the caused the gun barrel to explode. It is efficiency of the process will decline to barrel of which is reckoned to be more easily appreciated that the failure of that zero when the shock wave cannot catch than 160 metres long. Curiously, the project may have sprung from the diffi­ the accelerated projectile. That limit, a device was bound for Iraq on the platform culty of timing the explosion of the inter­ function of the density of gases in the of an open truck. mediate propellant charges with sufficient barrel and of their composition, could Those who know about artillery design accuracy. The amount of the intermediate easily allow the terminal velocity of 600 m say that such a barrel is inexplicable on charge is important, but the timing of its S·l to be exceeded four-fold after 15 inter­ conventional grounds. The most effective detonation immediately on the heels of mediate renewals of the shock-wave. high-velocity weapons now in service, the passing projectile must be crucial. Whether that was really what Iraq was notably the South African long-range gun, That is where the detonating capacitors about will probably remain publicly are built with barrels some 45 times longer impounded at London Airport earlier in unknown. The originator of the project than the diameter of the projectiles they the month may be relevant. It is neither seems to have been a Dr Gerald Bull, of are designed to fire. Previous generations here nor there that the real goods had Canadian origin but with US citizenship, of weapons have worked with smaller been replaced by fakes by collaboration who was murdered by gunmen outside his ratios of barrel-length to calibre - 40 or between the US and British intelligence Brussels apartment three weeks ago. even less. agencies - the originals must have been Bull's company, International Space That there should be some such limit is intended for the accurate timing of explo­ Systems, seems to have placed contracts understandable. The function of a gun sions of some kind. In the Iraqi experiment, for the gun components with their British barrel is to allow the continued accelera­ if that is what it was, the ideal would be manufacturers. Previously, he had been tion of the projectile by the shock-wave that each section of the gun barrel would the driving force for the joint US-Canadian from the propellant charge and eventually be joined to its successor by a short section 'HARP' project for sending rocket­ from simple hydrostatic pressure, which carrying a cylindrical explosive charge, assisted projectiles high into the atmo­ must diminish along the length of the which would allow of 15 intermediate sphere and even into orbit and for the barrel. Plainly there will be a point at explosions. It will be interesting to see development of the South African artillery which friction between projectile and whether manufacturers in the West have piece. barrel will be greater than the decreased been making to the order of Iraqi agencies Bull's competitors in the arms trade propellant pressure, at which point the cylindrical steel sections of 1 m internal have a great respect for his ingenuity; one barrel might usefully be terminated. diameter with concentric chambers for said on the telephone this week that "if Moreover, there are also limits to what carrying internal propellant charges. Gerry said it could be done, I'd believe can be done by increasing the propellant Would such an arrangement suffice to him and not the others". But the general charge; the breech mechanism has to be give the Iraqi gun a range significant in the opinion seems to be that Bull was more more robust, but the propagation of a Middle East? Because the range of a gun interested in gun-launched rockets and in detonation in the solid propellant may be (neglecting atmospheric resistance) is undersized projectiles than in more so much slower than that of shock-waves roughly proportional to the square of the complicated devices. On this occasion, along the barrel that extra propellant muzzle velocity, the auguries are good, time may not tell. John Maddox NATURE· VOL 344 . 26 APRIL 1990 811