RBL 7 Inch Armstrong Gun - History

History

This method had already proved successful in the RBL 12 pounder 8 cwt field gun, and the British Government requested it be implemented for heavy guns despite Armstrong's protests that the mechanism was unsuited to heavy guns :

"The threatening aspects of the continent required that large rifled guns should be procured for naval and siege purposes. I was therefore called upon to produce 40-pounders and 100-pounders without having had an opportunity of testing the patterns by previous trials, though I had stated in my original report that I apprehended that the application of breech-loading to large guns would involve an application of parts which would be inconveniently heavy to handle... I was at first in hopes that the same material which had been used and found to be sufficient for the 40-pounder, would be found equally suitable for the 100-pounder; but that turns out not to be the case. The vent-piece for the 100-pounder continues still to be a difficulty". Sir W Armstrong to the Select Committee on Ordnance in 1863.

The gun as first made weighed 72 cwt (8,064 lb) but the heavier 82 cwt (9,184 lb) version, incorporating a strengthening coil over the powder chamber, was the first to enter service in 1861. It was intended to replace the smoothbore muzzle-loading 68-pounder gun, and was intended to be Britain's first modern rifled breech-loading naval gun. The lighter 72 cwt version eventually entered service in 1863 for land use only.

The British government's Select Committee on Ordnance held lengthy hearings in 1862 and 1863 on the relative merits of the Armstrong breechloaders compared to other breechloaders and muzzle-loaders. It finally announced :

"... the preponderance of opinion seems to be against any breech-loading systems for the larger guns"

It was considered that with a maximum gunpowder propellant charge of only 12 pounds (soon reduced to 11 lb for the 82 cwt gun and 10 lb for the 72 cwt gun) the gun was incapable of a high enough muzzle velocity to penetrate the armour of enemy ships :

"These guns can only be fired with comparatively small charges, and therefore their projectiles would do no injury to ironclad vessels, but their shells would no doubt be most destructive to wooden ships." : the sarcastic comment of Lieutenant-Colonel C H Owen, Royal Artillery, reflecting the establishment opinion in 1873.

Critics also considered that the manual labour needed to raise the heavy (136 lb) vent piece out of the breech before reloading was an unnecessary combat impediment. Another objection raised was that obturation (i.e. sealing of the breech on firing) depended on how tightly the gunners turned the breech screw after loading :

"My objection has been to the Armstrong breech-loader. My objection to that is, that the breech-plug is only a valve; and the first principle of every valve, whether the vessel contain water or oil, or gas, is that the pressure of that fluid should press the valve tighter. Now Sir William Armstrong's breech-loader is on a diametrically opposite system; nothing there confines the gas but the actual amount of labour expended in the screwing up of the breech. If the gas is stronger than the man, aided by the screw, the gas will escape"... Captain Blakely to the Select Committee on Ordnance.

As these limitations were imposed by the current Armstrong breechloading design, and as no other suitable breechloading mechanism was available, production of the 110-pounder was discontinued in 1864 and Britain reverted to muzzle-loading heavy guns.

The abandonment of the Armstrong breech-loading design led Britain to begin a major program of building rifled muzzle-loaders to equip its fleet. The Armstrong 110-pound gun was succeeded by various RML 7 and 8-inch guns. 7-inch Armstrong breech-loaders under construction at the time of cancellation were completed as RML 64-pounder muzzle-loaders. However, the gun construction method developed by Armstrong for breech-loaders, of a wrought-iron "A" tube surrounded by wrought-iron coils, was considered sound and was retained for the first generation of new rifled muzzle-loaders in the mid-1860s.

When Britain returned to breech-loaders in 1880 it used the Elswick cup and the French De Bange obturation systems, both of which used the power of the gun's firing to achieve obturation rather than manual labour.

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