Back to the Drawing Board: Rifled muzzle-loading artillery (RML)

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David Porter on military history’s doomed inventions

The mid 19th century saw a revolution in naval weapons technology – smooth-bore muzzle-loading artillery, which had changed little for over 300 years, was suddenly supplanted by far larger rifled guns firing steel armour-piercing shot and explosive shells to ranges far beyond anything achieved even 50 years earlier.

One of the many Parrott RMLs to suffer a burst barrel – a 300-pdr, Morris Island, South Carolina, 1863.
One of the many Parrott RMLs to suffer a burst barrel – a 300-pdr, Morris Island, South Carolina, 1863.

However, the new artillery was pushing the technology of the era to its limits. This was emphasised during the American Civil War, when thousands of Parrott ‘rifles’ were produced by both sides for army and navy use.

These were almost all muzzle-loaders, ranging in size from 10-pdr light field guns to huge 300-pdr siege artillery pieces, and they acquired an evil reputation for bursting due to the brittle cast iron used in their construction.

A typical accident occurred on 24 December 1864 aboard the sloop USS Juniata during the bombardment of Fort Fisher when a 100-pdr Parrott gun burst, killing five men, and injuring a further eight. The New York Times later reported that shipboard fatalities alone due to Parrott gun mishaps numbered more than a hundred.

The Royal Navy had its share of problems with rifled muzzle-loaders. It had pioneered breech-loading rifled guns as early as 1861, when HMS Warrior was commissioned with 40- and 110-pdr Armstrong breech-loaders as part of her armament. But it was found they required very careful loading and could not be fired with charges as powerful as equivalent muzzle-loaders.

The Armstrongs had been regarded with suspicion by more conservative senior officers, who seized on these limitations and were able to persuade the Admiralty to adopt rifled muzzle-loaders, which could be produced in the ever-larger calibres needed to penetrate the armour of the new generation of ironclad warships entering service with the world’s major navies.


By the late 1860s, the latest British battleships were being armed with turretmounted 305mm (12in) RML guns firing shells weighing over 300kg (700lb). Ammunition of this weight required hydraulic powerloading through shafts from the lower deck and, although not appreciated at the time, this was potentially highly dangerous.

The risks became apparent in January 1879, when HMS Thunderer was at gunnery practice. Both guns in the forward turret were fired and run back hydraulically for reloading. In fact, one gun had misfired, but the blast and smoke of the other gun masked this, and the immediate operation of the hydraulic running-back gear concealed the absence of recoil.

The power-loading cycle rammed in fresh charges and shells, so that the left-hand gun now had two cartridges and two shells in the bore. On firing, it unsurprisingly burst, killing 11 men and injuring a further 35.

Initially, there was some controversy over exactly what had happened, but the undamaged gun was removed for trials at Woolwich Arsenal, where it was double-loaded and fired inside an armoured test emplacement. It broke up in virtually identical fashion, proving that the loading method was indeed responsible.

This marked the beginning of the end for British RML naval guns, which were rapidly phased out of service with the Royal Navy in favour of improved types of breech-loading artillery.

This article was published in the October/November issue of Military History Matters. To find out more about the magazine and how to subscribe, click here.

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