Cordite
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- The extinct tree is spelled Cordaites.
Cordite is a family of smokeless propellants made by combining two high explosives: nitrocellulose and nitroglycerin, that is it is a double-base propellant. However, Cordite N, a triple-base propellant was developed during World War II and is now used in large guns (see below). Cordite is legally classified as an explosive but it is normally used as a propellant for guns and rockets.
Cordite was developed in Great Britain in the late 19th Century and has been used since World War I by Britain and by British Commonwealth countries as a military propellant for firearms, artillery and naval guns. Its use was further developed in the early years of World War II, as 2 inch and 3-inch diameter solid-fuel rockets for launching anti-aircraft weapons[1]. Small Cordite rocket charges were also developed for Ejector seats made by the Martin-Baker Company.
[edit] Early history of smokeless powders
[edit] Poudre B
In 1886, French chemist Paul Vieille invented the first smokeless powder, called Poudre B (Poudre Blanche = white powder). It was made out of two forms of nitrocellulose (collodion and guncotton) softened with ethanol and ether and kneaded together, i.e. a single-base propellant. Three times more powerful than black powder and relatively free from vast quantities of smoke, Poudre B was a great improvement on black powder (or Poudre Noire = black powder).
The reason that Poudre B was smokeless is that the combustion products were mainly gaseous, compared to around 60% solid products for black powder (e.g. potassium carbonate, potassium sulfate, etc). It was immediately adopted by the French military but it tended to become unstable over time and this led to many accidents; for example two battleships, the Jena and the Liberté, blew up in Toulon harbour in 1907 and 1911 respectively.
[edit] Alfred Nobel and Ballistite
In 1887, Alfred Nobel invented and patented a smokeless propellant he called Ballistite, which was composed of 10% camphor, 45% nitroglycerin and 45% collodion (nitrocellulose), that is a double-base propellant. His patent specified that the nitrocellulose should be "of the well-known soluble kind". Over time the camphor tended to evaporate leaving an unstable explosive.
[edit] Nobel and Abel Patent dispute
Nobel sued Abel and Dewar over patent infringement (see Cordite Mk I below), eventually getting to the House of Lords in 1895 but lost because the words "of the well-known soluble kind" in his patent were taken to mean the soluble collodion and hence specifically excluded the insoluble guncotton.
[edit] Cordite formulations
[edit] Abel and Cordite (Mk I)
A United Kingdom government committee, known as the "Explosives Committee", chaired by Sir Frederick Abel, monitored foreign developments in explosives and obtained samples of Poudre B and Ballistite. Abel and Sir James Dewar, who was also on the committee, jointly patented in 1889 a new propellant consisting of 58% nitroglycerin, by weight, 37% guncotton and 5% vaseline in 1889. Using acetone as a solvent, it was extruded as spaghetti-like rods initially called "cord powder" or "the Committee's modification of Ballistite" but this was swiftly abbreviated to "Cordite". It was quickly discovered that the rate of burning could be varied by altering the surface area of the cordite. Narrow rods were used in small-arms and gave relatively fast burning, while thicker rods would burn more slowly and were used for longer barrels such as those used in artillery and naval guns.
This is now obsolete—as it caused excessive gun barrel erosion—other formulations of Cordite were produced and the original Abel-Dewar formulation became known as Cordite Mk I.
[edit] Cordite MD
Cordite, Ballistite and Poudre B continued to be used in different armed forces for many years but Cordite gradually became predominant. One problem was that early versions of cordite quickly eroded gun barrels. To combat this the British changed the composition to 65% guncotton and 30% nitroglycerine (keeping 5% vaseline) shortly after the end of the Second Boer War. This was known as Cordite MD (= MoDified). Cordite MD is also obsolete.
[edit] Cordite RDB and Cordite SC
During the World War I acetone was in short supply in Great Britain and a new experimental form was developed[2]. This was Cordite RDB (= Research Department formula B); which was 52% collodion, 42% nitroglycerin and 6% vaseline (Petroleum jelly). It was produced at HM Factory, Gretna[2]; and the Royal Navy Cordite Factory, Holton Heath. It tended to become unstable if stored too long. Once acetone production increased, by the use of fermentation (see Chaim Weizmann), the older form of Cordite, Cordite MD, was brought back for Royal Navy use.
Research on solvent-free Cordite RDB continued primarily on the addition of stabilizers, which led to the type commonly used in World War II onwards. In Great Britain this was known as Cordite SC (= Solventless Cordite). Cordite SC was produced in different shapes and sizes so the particular geometry of Cordite SC was indicated by the use of letters or numbers, or both, after the SC. For example SC followed by a number was rod-shaped cord, with the number representing the diameter in one-thousandths of an inch. SC T followed by two sets of numbers was tubular propellant with the numbers representing the two diameters in one-thousandths of an inch.
Two-inch (approximately 50 mm) and three-inch (approximately 75 mm) diameter rocket Cordite SC charges were developed in great secrecy in the later stages of WW II for anti-aircraft purposes—the so-called Z-gun batteries[1].
Great Britain changed to metric units in the 1960s so there was a discontinuity in the propellant geometry numbering system.
[edit] Triple-base propellant and Cordite N
An important development during the Second World War was the addition of another explosive, nitroguanidine, to the mixture to form triple-base propellant or Cordite N. This solved two problems with the large naval guns of the day as fitted to capital ships. Nitroguanidine produces large amounts of nitrogen when heated, which had the benefit of reducing the muzzle flash and its lower burning temperature greatly reduced the erosion of the gun barrel.
[edit] Cordite charge design
[edit] Cordite manufacture
In Great Britain Cordite was developed for military use at the Royal Arsenal Woolwich and at the Waltham Abbey Royal Gunpowder Mills from 1889 onwards.
In World War I a great Cordite factory, HM Factory, Gretna, which straddled the Scotland-England border at Gretna to manufacture Cordite for the British Army and for British Commonwealth forces. A separate factory, The Royal Navy Cordite Factory, Holton Heath, was opened to manufacture Cordite for the Royal Navy. Both the Gretna and the Holton Heath Cordite factories closed at the end of World War I.
By the start of World War II Holton Heath had reopened and an additional factory for the Royal Navy, The Royal Navy Propellant Factory, Caerwent, opened at Caerwent in Wales. A very large Royal Ordnance Factory, ROF Bishopton, was opened in Scotland to manufacture Cordite for the British Army and the Royal Air Force. A new Cordite factory at Waltham Abbey and two additional ROF's—ROF Ranskill and ROF Wexham—were also opened. Cordite produced in these factories was sent to Filling Factories for filling into ammunition.
Additional sources of propellant were also sought from the British Commonwealth. The United States did not use Cordite, however, several ammunition filling factories were set up in Canada to fill American propellant supplied by the USA under Lend-Lease. India, Pakistan and Australia were also approached.
[edit] Other British Cordite factories in World War II
The British Government set up additional cordite factories, not under Royal Ordnance Factory control but as Agency Factories run on behalf of the Ministry of Supply. The famous company of ICI Nobel at Ardeer was asked in 1939 to construct and operate six factories in southern Scotland. Three of these six were involved in cordite or firearm-propellant manufacture. The works at MS Drungans (Dumfries) produced guncotton that was converted to cordite at MS Dalbeattie (triple-base cordite) and at MS Powfoot (monobase granulated guncotton for small-arms). A third of British cordite produced between 1942 and 1945 came from these factories alone. ICI ran a similar works at Deer Park near Melbourne in Australia.
[edit] Notes
[edit] References
- Brown, Donald, (1999), Somerset v Hitler: Secret Operations in the Mendips 1939 - 1945, Newbury: Countryside Books. ISBN 1-85306-590-0.
- Cocroft, Wayne D., (2000), Dangerous Energy: The archaeology of gunpowder and military explosives manufacture. Swindon: English Heritage. ISBN 1-85074-718-0.
- Davis, Tenney L., (1943). The Chemistry of Powder and Explosives, Volume II, New York: John Wiley & Sons, and London: Chapman & Hall.
- Ministry of Munitions of War, (1919). H.M. Factory, Gretna: Description of plant and process. Dumfries: J. Maxwell and Son, for His Majesty's Stationery Office.
