A Supergun is a generic term for any piece of artillery which is designed to radically outperform the current state of the art. In specifics, it is usually used to refer to the designs of Gerald Bull, as chronicled in his node and in the HBO movie named, appropriately, Supergun. It should be noted, however, that they were not his idea; rather, he espoused using them for space launch and other 'eclectic' uses, and he performed a great deal of physics, metallurgical, ballistics and aerodynamics research towards their construction. In so doing, he popularised the notion of the 'supergun' to the point where laymen can point to made-for-TV movies and say 'oh, sure, a supergun.'
In general, these days, a supergun is a projectile weapon designed to use a long barrel and (usually) 'pumping' auxiliary firing chambers to accelerate a projectile to velocities unachievable by a single propellant charge.
For any single-charge projectile weapon with a fixed projectile and charge size, there is a maximum barrel length beyond which additional length not only fails to increase the muzzle velocity of the projectile, but will also begin to degrade said velocity due to friction and limits of gas expansion. Thus, to increase the range of a single-charge artillery piece without lowering payload, one must first increase the charge strength. This, in turn, will typically require at least additional testing - and at the worst, new materials science - in the construction of the barrel, breech and operating mechanisms. This is the reason that naval cannons of similar general capability tend to converge on a common length over history.
While the idea may be traced all the way back to Jules Verne's 'Moon Gun' in From the Earth to the Moon, the original engineering, as far as I have been able to determine, can be be laid at the feet of a pair of U.S. Army boffins named Lyman and Haskell in the 1880s. This idea, which forms the basis of the supergun concept, was that there is no reason one cannot attach additional combustion (firing) chambers along the barrel of the weapon, joining in at right angles or angled slightly rearward. These chambers would fire as the projectile passed them; this would permit the maintenance of high pressure throughout the entire barrel run, as opposed to a barrel pressure that dropped steadily as the projectile travelled along it due to the increasing volume of space behind it.
Some bad ASCII art:
( O ) --> auxiliary chamber
( \, / ) --> chamber connections
( == ) --> barrel section
( X ) --> main firing chamber
( >>> ) --> Projectile's flight
O O O
-----\ \ \ \
X =============================== >>>
-----/ / / /
O O O
This got around most of the problems of 'supersizing' artillery. The barrel metallurgy need not be extreme, as no part of the barrel would undergo more stress than was normally taken by the highest pressure during a regular firing. The speed and/or payload of the weapon could be adjusted by varying the number of additional firing chambers rather than changing the entire design. No exotic propellants with higher expansion velocities were needed. The major downside to the supergun was that it was big, and in addition, the pressure-bearing parts of the gun needed to be machined and contain joins (where the barrel sections were joined, as well as where the additional chambers met the barrel). Finally, firing it was more complex because each auxiliary chamber needed to fire after the projectile passed it, but before the projectile had moved far enough away for it to be of little use.
The final problem was the one that scotched the original version of the supergun. Lyman and Haskell had relied on the expanding propellant gases behind the projectile to ignite the auxiliary firing chambers; however, in practice, the gases tended to 'leak around' the projectile (due to rifling grooves and simple spacing between the projectile and the barrel). This would ignite the auxiliary charges before the projectile reached them, resulting in a net loss of velocity as the pressure ahead of the projectile was increased. It wasn't until the next major attempt that this problem was solved.
The next supergun can be more precisely called by its original name, the German Hochdruckpumpe (High Pressure Pump, which was a remarkably descriptive codename). In 1943, the original HDP (Hochdruckpumpe) design was proposed to the German government by an engineer named Conders, who was working at a steel foundry in Leipzig. Conders' original realization was the Lymans and Haskell's gun could be operated by synchronizing the auxiliary charges with electrical ignition systems, using propellants that would not detonate when the initial gas wave hit them.
With the backing of Albert Speer (Hitler's Minister of Munitions),the HDP progressed through a series of test designs at Peenemunde on the Baltic Coast. Eventually, based on their performance (despite initial disappointments in muzzle velocity and problems with rupturing barrels), Hitler ordered the construction of a battery of 25 HDP guns at Mimoyecques, along the Normandy Coast. These guns were to be buried at an angle in the wall of a quarry, and were intended to rain shells down on London at a rate of 200 per hour, and were referred to collectively as the 'V-3', standing for Vergeltungswaffen-3, or 'reprisal weapon number 3'. They were to carry on the campaign of terror on Britain begun by the V-1 Buzz-bomb and V-2 Rockets. See the most excellent V-3 node for more info (and overlap).
Although that site never became operational (it was destroyed by 617 Squadron, the RAF pinpoint bombing group known as The Dam Busters for their first and most famous raid) two smaller HDP guns were in fact fired in anger in December 1944 and January 1945, against Luxembourg, from a range of approximately 44 km. They weren't militarily effective, due mostly to their being unready for use at the opening of the offensive (known as the Battle of the Bulge), and to disrupted rail transport depriving them of adequate ammunition supply. Nevertheless, they did work; a total of 183 shells were fired at Luxembourg, and 143 detonated within its borders. 10 civilians were killed and 35 wounded. While this isn't many, it is not at all bad if one considers the low marginal cost of supplying the ammunition and charges to the guns - far more resources were spent on V-1 and V-2 production and operations for less result. Had the weapons been given another month of preparation and final tweaking (they were, after all, an untested system) as well as a steady ammunition supply, they could have wreaked havoc inside Luxembourg. Whether that would have affected Allied military operations is questionable, especially since they were extremely difficult to retrain.
In any case, Gerald Bull was starting with this (considerable) mass of effort and information already at his disposal. His particular contribution involved the scaling-up of the German designs, as well as applying modern materials and engineering, to build versions which were intended to throw shells hundreds of miles. His initial tests, conducted off the coast of Barbados and using a gun constructed out of existing gun barrels, were able to throw a shell to one hundred and eighty-two km of altitude - commensurate with his desire to sell the device as a satellite launching system. These initial tests were funded as the HARP, or High Altitude Research Program, by the U.S. and Canadian governments.
Despite successful tests, the pressures of the Vietnam War caused his backers to withdraw government funding from HARP. Bull was successful in transferring the program to a private consulting firm he set up in Belgium, where he continued to work on it, garnering funds from private arms research contracts.
Bull's research career was checkered, as is noted on his node, due to his willingness to sell his skills to pretty much any regime that would pay him in order to finance his dream of space launch. Eventually, he had sold supergun concepts and prototypes to Iraq, as well as conventional artillery improvements (such as base bleed and base burn ) to South Africa, North Korea, China, Syria, Israel and Iraq - not all of whom saw eye to eye. According to the James Adams book (see sources, below) and the resulting HBO film, it was his sale of missile technology upgrades to Iraq (he did much of the aerodynamic work on the Al-Husayn expansion of the SCUD missile, as well as designed self-propelled artillery pieces for them) that brought the Mossad down on him; he was assassinated outside his apartment in Brussels, Belgium in 1990.
After the First Gulf War, the U.N. Special Commission received documents on July 18th, 1991 from Iraq which stated that Iraq had, indeed, constructed a 45-meter sub-size supergun prototype (nicknamed 'Baby Babylon') with a 350-mm bore, and had been designing and importing components to build a much larger (1000-mm bore) version known as 'Babylon'. U.N. teams located and destroyed components of the larger gun, the existing smaller gun, and stored propellant and manufacturing facilities for ammunition and propellant for both. Testimony before the commission from defectors indicated that the gun was too inaccurate to be used for conventional bombardment (the potential range of the Iraqi superguns was estimated to be around 1,000 km) and that the guns were intended for the delivery of WMD against Israel and American targets in Kuwait and Saudi Arabia. They further indicated that the Iraqis were researching means of using the superguns to launch weapons designed to destroy or blind hostile spy satellites - bringing Bull's vision almost full circle.
The Supergun concept remains one of interest to various militaries. The major problem with using the supergun as a weapon is its size; in order to safely anchor it and ensure it cannot shift during firing, it pretty much has to be mounted directly to the ground along an incline. While the fixed nature of its resulting aimpoint can be mitigated through the use of self-navigating projectiles (Competent Munition, e.g.), few of the major modern military powers have the need for a single, point-target system such as this. Improvements to various commercial satellite launch systems have forestalled much research into the launch gun concept.
There are, of course, conflicts which offer target sets amenable to supergun use (the usual candidates as of 2003 include the North Korea vs. Seoul dyad and the China vs. Taiwan axis). However, the Korean standoff doesn't really require them (practically all of Seoul is within 25 miles of the North Korean border, a range easily attained by modern artillery, especially that improved by Bull's work). The Taiwan Straits are a more attractive application, representing a target set perhaps 100 nautical miles or more distant from the mainland. However, the Chinese are quite handy at the design, manufacture and fielding of short- to intermediate-range ballistic missiles which, while they may be more expensive per shot, are much more flexible since you can move them around and retarget them.
In any case, there remains a strong possibility that a military 'supergun' may crop up in the near future; however, given that they are large, fixed, and fragile and that their use is easily backtracked using decent radar, counterbattery fire using missiles or airstrikes would be easily made effective.
- V-3 and Gerald Bull
- Luxembourg National Military Museum virtual tour: http://www.nat-military-museum.lu/pageshtml/museumspecial.html
- Astronautix.com : http://www.astronautix.com/lvs/v3.htm
- Norfolk and Suffolk Aviation Museum's Joe Kennedy page: http://www.aviationmuseum.net/Joe_Kennedy.htm (Mimoyecques was Kennedy's target on his final, fatal mission).
- 617 Squadron: The Dam Busters by Paul Brickhill; Pan Books, 1983. (ISBN: 0-330-37644-6)
- German Artillery of World War Two; Ian Hogg Greenhill Books, 1997.
- Global Security's Gerald Bull/Supergun page: http://www.globalsecurity.org/wmd/world/iraq/supergun.htm
- Bull's Eye: The Assassination and Life of Supergun Inventor Gerald Bull James Adams; Times Books, 1992