EOC 12-inch L/23.5

EOC 12-inch L/23.5
As depicted in March 1877
Type	Naval artillery
Place of origin	United Kingdom
Service history
Used by	None (prototype)
Production history
Designer	Elswick Ordnance Company
Manufacturer	Elswick Ordnance Company
Produced	1877
No. built	1
Specifications
Mass	39 long tons (40 t)
Length	282 inches (7.16 m) L/23.5
Caliber	12 inches (30.5 cm)
Muzzle velocity	1,650 feet per second (500 m/s)

The EOC 12-inch L/23.5 or '39-ton breechloading gun' or '40-ton breechloading gun', was an experimental breechloading gun designed and manufactured by the Elswick Ordnance Company also known as Armstrong. The gun was made to profit from recent discoveries about how gunpowder behaved. These required longer guns and made muzzleloading troublesome. The gun seems to have been a failure.

Context

The 12.5-inch 38-ton RML

Main article: RML 12.5-inch 38-ton gun

The development of the EOC 12-inch L/23.5 gun, took place at about the same time as experiments with a muzzle-loading gun of almost the same weight, the RML 12.5-inch 38-ton gun. This was basically a RML 12-inch 35-ton gun that had been given a slightly higher caliber and was significantly lengthened to make better use of new kinds of gunpowder. Initial results were very good. In October 1876, the 12.5-inch 38-ton RML was then tested against armor at Shoeburyness. With a charge of 130 pounds (59 kg), a 800 pounds (360 kg) Palliser shell was fired. It went through the target, which consisted of 19.5 inches (500 mm) of iron and 10 inches (250 mm) of teak. Velocity was estimated at 1,420 feet per second (430 m/s). This was again a very good result and plans were made to widen the chamber of the gun.

At the time, 'chambering' a gun meant that its chamber got a diameter that was significantly wider than its caliber. For the 12.5-inch gun this resulted in a chamber diameter of 14 inches (35.6 cm). A test in March 1877 (i.e. after the below test of our L/25.5 gun) proved that this allowed an increased charge of 200 pounds (91 kg) of pebble powder. The results were contested when it came to velocity and impact. However, with regard to loading the gun through the muzzle, the challenges were obvious. The first charge could not be rammed down and had to be blown out. The second charge could not be fit in the chamber and stuck out a bit, negatively impacting the result.

The new Armstrong breechloading system

Meanwhile, the Elswick Ordnance Company (EOC) had been working on creating a new breechloading mechanism. This was based on the interrupted screw system used by the French navy. The obturation method differed. For this the EOC used a steel cup or saucer attached to the end of the breech screw. When the charge exploded, it expanded this cup, which then came to fit on a copper ring in the chamber, forming a seal against escaping gas.

Development of the EOC 12-inch L/23.5

Development

Development of the EOC 12-inch L/23.5 started in 1875. It weighed about the same as the RML 12.5-inch 38-ton gun. However, its length of bore of 264 inches (6.7 m) or L/22 showed that it was based on very different ideas than those behind the RML 12.5-inch 38-ton gun with its length of bore of only 198 inches (5.0 m) or L/16. The similarity between the charges of the guns was as deceiving as their weight. In February 1877 (below), the EOC gun fired with a charge of 180 pounds (82 kg), one month later the chambered Woolwich gun fired with a charge of 200 pounds (91 kg) (above).

The deceivingly similar charges can be explained by the fact that it was possible to chamber the RML 12.5-inch 38-ton gun without changing the rest of the gun. On the other hand, the EOC gun could get a longer chamber, because its longer barrel was able to 'consume' the energy of slower burning gunpowder. Both circumstances led to the EOC gun using a high charge without chambering the gun. I.e. the EOC 12-inch L/23.5 was not chambered.

Tested near Elswick

In February 1877, the EOC 12-inch L/23.5 and a smaller 4.75 inches (121 mm) EOC gun were tested at the Elswick proof ground, some forty miles north of Newcastle. Among those present were: General Campbell, director-general of Artillery and Stores; Colonel Younghusband, Superintendant of the Royal Gun Factory; the naval attachés of: France, Austria-Hungary, Russia, Italy, Brazil; Captain Jessen Director of Danish Naval Ordnance; Captain Müllertz sent by Denmark; Captain Garcia of the Spanish Naval Commission; as well several others.

The tests involved three shots with the 12-inch L/23.5 with measurements of velocity and peak gas pressures. With a charge of 160 pounds (73 kg) velocity measurement failed, peak pressures were 15.0 tons per square inch (2,286 atm) at the top of the chamber and 15.1 tons at the bottom. With a charge of 170 pounds (77 kg), velocity was 1,563 feet per second (476 m/s) and pressures were 17.1 at the top and 18.3 ton at the bottom. With a 180 pounds (82 kg) charge, velocity was 1,615 feet per second (492 m/s) and pressures were 18.6 at the top and 18.7 ton per square inch (2,850 atm) at the bottom. One can compare these results with the test of the Krupp 30.5 cm MRK L/25 in 1878.

As the news showed, the tests were not only about the power of the gun, but also about using the Armstrong breech on heavy guns. After the test, it was said that this 'worked perfectly, the breech being easily opened without assistance of any sort, by one man, and with great rapidity. The escape of gas was entirely prevented'.

The results were very promising. However, they said nothing about the endurance of the gun or the breech. For that a durability test (prolonged firing) was required.

A failure?

After the February 1877 tests, it became rather quiet about the EOC 12-inch L/23.5. An August 1878 overview of powerful modern British guns mentioned an Elswick breechloading gun of 6-inch which fired a 70 pounds (32 kg) projectile with the enormous speed of 2,000 feet per second (610 m/s). It also mentioned an Elswick 8-inch 11.5 tons gun firing a 180 pounds (82 kg) projectile with the same velocity. Our EOC 12-inch L/23.5 was not mentioned.

In July 1878, Krupp successfully tested three heavy artillery pieces in Meppen. The Krupp 30.5 cm MRK L/25 was not the main subject of the test, but its caliber made that it figured in an official comparison of guns of about 12 inch. The EOC 12-inch L/23.5 was also mentioned, as were a French 12.6 inch 38-ton breechloader, an Italian breechloader, and a 12-inch Russian one of 40-tons. The overview concluded that the chambered RML 12.5-inch 38-ton gun mark II made by the Royal Arsenal, was the most powerful of these guns.

During the August 1879 Meppen tests, Krupp showed that it had caught up in chambering guns. Its prototype 24 cm MRK L/25.5 of 18 ton created a sensation as it was just as powerful as the above 12-inch guns. Only the most recent British guns, like the BL 9.2-inch Mk I – VII naval gun then under development; the EOC 8-inch 11.5-ton gun; and the EOC 9-inch 18-ton gun, were of comparable efficiency. Obviously, the EOC 12-inch L/23.5 had been overclassed by breechloaders using much higher charges.

When both developments, i.e. the need for longer guns and the advantages of 'chambering' a gun, became clear, the British artillery establishment had to change its stance on breechloading. An obvious reason to do this was that muzzleloaders longer than the 38-ton gun could not be handled in existing works, because they had to be brought in to reload.

A somewhat later lecture about the Meppen tests primarily focused on a comparison between the 40 cm MRK L/25 and the Elswick 100-ton gun. In the audience Stuart Rendel then referrred to the EOC 12-inch L/23.5 breechloader made almost five years earlier.

Characteristics

Labels

On the 1877 engraving, the gun is called a 39-ton gun. Later on, it was called a 40-ton gun, because this was more convenient.

Technical

The 12-inch L/23.5 had a caliber of 12 inches (30.5 cm). The barrel had a length of 282 inches (7.16 m) or L/23.5 with a length of bore of 264 inches (670.6 cm) or L/22. The gun weighed 39 long tons (40 t). There were 45 grooves of the polygroove type. The twist rate was progressive, increasing from L/100 to L/45, meaning that at the muzzle, the projectile made a turn on its axis every 45 feet (14 m). (Really every 45 calibers, with the caliber happening to be one foot)

The gun fired a 700 pounds (320 kg) projectile. This used copper driving bands and a copper centration bourrelet. The driving band was an attached gas-check, which was pushed into the grooves by the force of the explosion. With charges of 170 pounds (77 kg) and 180 pounds (82 kg) of pebble powder, this reached a mean velocity of 1,606 feet per second (490 m/s) and 1,650 feet per second (500 m/s).

References

• "A new Breech-Loader". Army and Navy Gazette: Journal of the Militia and Volunteer. 1877. p. 118.
• Brassey, Thomas (1882), The British Navy: Its Strength, Resources, and Administration, vol. II, Longmans, Green, and Co. London
• "The 81-ton gun". The Engineer. XL. The Engineer, London: 211–212. 1875.
• "Several articles". The Engineer. XLII. The Engineer, London: 269. 1876.
• "Several articles". The Engineer. XLIII. The Engineer, London: 134, 203. 1877.
• Inglis, T. (1878). "Targets for the Trial of Recent Battering Ordnance part IV". Professional Papers of the Corps of Royal Engineers. II. The Royal Engineer Institute: 185–202.
• Inglis, T. (1880). "Targets for the Trial of Recent Battering Ordnance". Professional Papers of the Corps of Royal Engineers. IV. The Royal Engineer Institute: 169–194.
• King, James Wilson (1881), The War-ships and Navies of the World, A. Williams and Company, Boston
• "Ordnance and Naval". Van Nostrand's Eclectic Engineering Magazine. XVI. D. Van Nostrand publisher, New York: 478. 1877.
• Orde Brown, C. (1881). "Lessons to be learned from Krupp's Meppen Experiments of 1879". Journal of the Royal United Service Institution. XXIV. W. Mitchell and Co., London: 61–80.
• Rendel, Stuart (1875), The Question of the Guns as now debated, Spottiswoode and Co. London
• Simpson, E. (1880). "Wants of the Navy - Cannon I - III". Naval Organization and Administration: Pamphlet Collection. The United Service. p. 647–54.