View source for Rifled breech loader

{{Short description|Class of artillery}}
{{More footnotes|date=February 2021}}
{{Cannon}}
A '''rifled breech loader''' (RBL) is an [[artillery]] piece which, unlike the [[smoothbore]] [[cannon]] and [[rifled muzzle loader]] which preceded it, has [[rifling]] in the barrel and is loaded from the [[breech-loading weapon|breech]] at the rear of the gun.

The spin imparted by the gun's [[rifling]] gives projectiles directional stability and increased range. Loading from the rear of the gun leaves the crew less exposed to enemy fire, allows smaller gun emplacements or turrets, and allows a faster rate of fire.

These rapidly improving breech systems and the powerful new guns they facilitated led to an [[arms race]] in [[fortification]] and [[ironclad]] warship design that led to the [[battleship]] class of [[HMS Dreadnought (1906)|HMS ''Dreadnought'']] and continued until the start of [[World War I]].

==Overview==
The major problem to be solved with breechloading artillery was [[obturation]]: the sealing of the breech after firing to ensure that none of the [[gas]]es generated by the [[burning]] of the [[propellant]] (initially [[gunpowder]]) escaped rearwards through the breech. This was both a safety issue and one of gun performance – all the propellant gas was needed to accelerate the projectile along the barrel.

The second problem was speed of operation – how to close the breech before firing and open it after firing as quickly as possible consistent with safety.

Two solutions were developed more or less in parallel, the "screw breech" block and "sliding wedge" or "sliding block".

[[File:Oda Nobunaga swivel breech loading gun.jpg|thumb|left|A [[Japan]]ese swivel breech-loading gun of the time of [[Oda Nobunaga]], 16th century.]]
At the time of development of the first modern breechloaders in the mid-19th century, gunpowder propellant charges for artillery were typically loaded in cloth bags, which combusted totally on firing. Hence, unlike with a metal rifle cartridge, the breech mechanism itself somehow needed to provide obturation.

The early "screw" mechanisms for sealing the breech consisted of threaded blocks which were screwed tightly into the breech after loading, but the threads themselves were insufficient to provide a gas-tight seal. This was further complicated by the need to screw and unscrew the breech as quickly as possible; this was met by the "[[interrupted thread]]" breech block, where the block circumference was alternately threaded and left unthreaded at a slightly smaller diameter to allow the whole block to be fully inserted and rotated a fraction to lock it. Hence if the block circumference was divided into two sets of threads and gaps, the block only needed to be rotated ¼ turn to lock it instead of several turns. The tradeoff was that only ½ the block's circumference was threaded, reducing the security accordingly.

The other possibility of sealing the breech was to enclose the propellant charge in a metal cartridge case which expanded on firing and hence sealed the breech, leaving the breech-block merely needing to lock the cartridge case in place. This was more easily accomplished by sliding the block in behind the cartridge case through a vertical or horizontal slot cut through the rear of the breech : the "sliding wedge" or "sliding block" breech.

==History==

===Early breechloaders===
[[File:Чертёж_к_статье_«Варендорф»._Военная_энциклопедия_Сытина_(Санкт-Петербург,_1911-1915).jpg|thumb|right|Wahrendorff breech]]
The very first [[cannon]]s of the [[Middle Ages]] were breech loaded, with [[gunpowder]] and shot contained in pots dropped at the back of the barrel, but the poor seals made them dangerous, and they wore quickly and could not be scaled to larger weapons. Until the 19th century, mainly [[Muzzle-loading|muzzle-loaders]] were used.

In 1837,  [[Martin von Wahrendorff]] patented a design for a breech-loader with a cylindrical breech plug secured by a horizontal wedge; it was adopted by Sweden in 1854. Independently, [[Giovanni Cavalli]] first proposed a breech-loader gun in 1832 to the [[Sardinian Army]], and first tested such a gun in 1845.

===Armstrong screw breech===
[[File:RBL 7 inch Armstrong breech diagram.jpg|thumb|right|[[Armstrong gun]] screw breech.]]
Advances in metallurgy in the industrial era allowed for the construction of rifled breech-loading guns that could fire at a much greater [[muzzle velocity]]. After the British artillery was shown up in the [[Crimean War]] as having barely changed since the [[Napoleonic Wars]] the industrialist [[William Armstrong, 1st Baron Armstrong|William Armstrong]] was awarded a contract by the government to design a new piece of artillery. Production started in 1855 at the [[Elswick Ordnance Company]] and the [[Royal Arsenal]] at [[Woolwich]].<ref>{{cite journal|author=Marshall J. Bastable|title=From Breechloaders to Monster Guns: Sir William Armstrong and the Invention of Modern Artillery, 1854–1880|journal=Technology and Culture|year=1992|doi=10.2307/3105857|volume=33|issue=2|pages=213–247|jstor=3105857}}</ref><ref>{{cite web|url=http://www.gracesguide.co.uk/William_Armstrong|title=William Armstrong}}</ref>

His "Armstrong screw" breech involved loading the shell and gunpowder propellant charge in a cloth bag through the hollow breech screw, lowering a heavy block into a slot behind the powder chamber and screwing the breech screw tightly against the block to lock it in place. A degree of [[obturation]] was achieved via a cup on the face of the block being forced into a recessed ring on the chamber face. The system was in effect a vertical sliding block such as later used by [[Krupp]] in both horizontal and vertical form, with the crucial difference that Armstrong failed to make the progression to loading the powder charge in a metal cartridge, with the result that complete obturation was impossible.{{citation-needed|reason=As of 2023, some British guns still use bagged charges, e.g., Royal Ordnance L30|date=April 2023}}

[[File:Sagahan Armstrong gun used at the Battle of Ueno against the Shogitai 1868.jpg|thumb|left|The [[Armstrong gun]] was a pivotal development for modern artillery as the first practical rifled breech loader. Pictured, deployed by [[Japan]] during the [[Boshin War]] (1868–69).]]
Whatever obturation that was achieved relied on manual labour rather than the power of the gun's firing, and was hence both uncertain, based on an unsound principle and unsuited to large guns. Armstrong screw-breech guns were initially adopted by the [[British Army]] and [[Royal Navy]], but concerns about limited armour penetration of the shells due to limited maximum velocity, safety concerns with the breech blocks blowing out of guns, and higher skill levels demanded of gunners led the British Government to revert to [[muzzle-loading rifle|rifled muzzle-loaders]] from 1865 to 1880, when Britain finally deployed reliable screw breech mechanisms.

The Imperial Japanese Army used Armstrong cannon during the [[Boshin War]] to devastate the [[Aizu]] castle town and force its inhabitants to surrender quickly, and British Armstrong light field guns proved deadly against Chinese forces in the [[Second Opium War]]. However, the British Army and Navy preferred to revert to muzzle-loaders until larger high-powered breech-loaders with secure obturation systems that were relatively simple to operate were developed.

===Broadwell ring===
{{main|Broadwell ring}}
American engineer [[Lewis Wells Broadwell]] who worked as sales agent for the [[Gatling Gun]] Company in Europe replaced a papier-mache obturating cup in bag-loaded RBLs with a metallic gas ring and patented his invention in 1861, later perfecting it in 1864 and 1866; most countries paid royalties to Broadwell for the design, but in Germany the Krupp company stole it and used it for free.<ref>{{cite web | url=https://books.google.com/books?id=5g5AAAAAYAAJ&pg=PA882 | title=Reports on the Vienna Universal Exhibition of 1873: Presented to Both Houses of Parliament by Command of Her Majesty | year=1874 }}</ref>
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===French efforts===
[[File:Culasse systeme De Bange before 1923.jpg|thumb|right|[[Charles Ragon de Bange|de Bange]] interrupted screw breech.]]
In the meantime the French persevered with trying to develop breechloaders which combined faster loading than muzzle-loaders, high power, safety and solved the problem of obturation. The [[Lahitolle 95 mm cannon]] of 1875 with an [[interrupted screw]] breech met the first three requirements to a great extent and partially solved the obturation problem.

Finally the [[Charles Ragon de Bange|de Bange]] system introduced in 1877 solved the obturation problem with an asbestos pad impregnated with grease which expanded and sealed the breech on firing. The de Bange system formed the obturation system for all subsequent screw breeches to the present day. Britain adopted the de Bange breech when it returned to breechloaders in the early 1880s after some initial experiments with the inferior "Armstrong cup" obturation system.

Britain, France, and the United States preferred screw breeches for most calibres, but the major drawback of the de Bange interrupted screw as first implemented was that only half of the circumference of the breech block could be threaded, and hence it needed to be fairly long to achieve safe locking of the breech, which required three separate motions to open after firing; rotate to unscrew, retract the screw and swing to the side. Loading required the 3 operations in reverse. This was hence termed a "three motion block" and was slow to operate.

===Welin breech block===
{{main|Welin breech block}}
[[File:USN 14 inch railway gun Mk II open breech 1919 LOC 12666.jpg|thumb|left|[[Welin breech block|Welin breech]] with 4 sets of 3 thread steps.]]
While working as a weapons designer for [[Thorsten Nordenfelt]] in [[London]], [[Axel Welin]] solved this problem in 1889–1890 with his stepped [[interrupted screw]] [[Welin breech block]]. This had threads in sets of steps of increasing diameter so that instead of only half of the screw being threaded, the fraction threaded was '''number of steps / (1 + number of steps)''': i.e. if the block of a large gun had four steps of threads, 80% of the screw was threaded, allowing a much shorter screw and hence breech block. This allowed the block to be unscrewed and swung out in two motions – the "two motion interrupted screw" breech.

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===Bofors ogival screw===
[[File:Ogival screw Bofors.jpg|thumb|left|Bofors ogival screw breech]]
Also in the early 1890s, Arent Silfversparre of [[Bofors]] invented an ogival screw breech, similar to the Armstrong model in the way it eliminated the need to withdraw the screw before swinging it to the side. Bofors continued to use this in medium artillery into the 20th century.  The Elswick conical screw breech is very similar in concept.

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===The sliding block===
[[File:Krupp sliding block gun Philadelphia 1876.jpg|thumb|right|{{center|Krupp horizontal sliding block (left side) breech on large gun exhibited at the Centennial Exhibition, Philadelphia, 1876.}}]]
[[File:Figure423a Horizontal sliding-wedge breech operating mechanism.png|thumb|Diagram of the horizontal sliding wedge.]]

The German company [[Krupp]] in contrast, adopted "Horizontal sliding block" breeches, rather than screw breeches, for all artillery calibres up to {{convert|16|in|abbr=on}} naval guns. This was similar in some ways to the original "Armstrong screw"; the shot and powder cartridge were inserted through the open rear end of the breech into the gun bore, and a steel block was slid home into a horizontal slot cut through the breech to close the rear end of the breech.

However, unlike Armstrong, Krupp loaded the powder propellant in a metal [[cartridge (firearms)|cartridge]] case much like a large [[rifle]] cartridge, which expanded against the chamber wall on firing and effectively sealed the breech. The sliding block, in both horizontal and vertical forms, and metal cartridge case continued to be the preferred German breech system until after [[World War II]] (e.g. [[7.5 cm Pak 40]]), and is still used by some modern artillery.

===Quickfiring guns===
{{main|Quick-firing gun}}
[[File:1-InchNordenfelt4BarrelGunNavalActionDrawing.jpg|thumb|right|[[Woodcut]] depicting [[Royal Navy]] gunners in action with the [[1-inch Nordenfelt gun]], the first practical QF gun.]]
The first quick-firing light gun was the [[1-inch Nordenfelt gun]], built in Britain from 1880. The gun was expressly designed to defend larger warships against the new small fast-moving [[torpedo boat]]s in the late 1870s to the early 1880s and was an enlarged version of the successful rifle-calibre Nordenfelt hand-cranked "machine gun" designed by [[Helge Palmcrantz]]. The gun fired a solid steel bullet with hardened tip and brass jacket.

It was superseded for anti-torpedo boat defence in the mid-1880s by the new generation of [[Hotchkiss et Cie|Hotchkiss]] and Nordenfelt "[[British ordnance terms#Fixed QF|QF]]" guns of 47-mm and 57-mm calibre firing exploding "[[British ordnance terms#Common pointed|common pointed]]" shells weighing {{convert|3–6|lb|abbr=on}}.

The French firm Hotchkiss produced the [[QF 3 pounder Hotchkiss|QF 3 pounder]] as a light 47-mm naval gun from 1886. The gun was ideal for defending against small fast vessels such as torpedo boats and was immediately adopted by the RN as the "Ordnance QF 3 pounder Hotchkiss".<ref>British forces traditionally denoted smaller ordnance by the weight of its standard projectile, in this case approximately {{convert|3|lb|kg}}.</ref> It was built under licence by [[Armstrong Whitworth#Elswick Ordnance Company|Elswick Ordnance Company]].

Both the [[Hotchkiss et Cie|Hotchkiss]] and [[Nordenfelt]] guns loaded ammunition as a single cartridge with projectile, cartridge case and primer in a single unit. The cartridge case sealed the breech on firing and a vertical sliding wedge (block) locked it in place. These new guns incorporated recoil control devices which facilitated consistency of aim, allowed single-motion loading and could be fired as soon as the cartridge was inserted, and then ejected it after firing, these properties denoting a "quick-firing" gun. This set a new standard for artillery, and made firing cycles measured in seconds rather than minutes possible.

Britain used brass cartridge cases for all calibres up to 6&nbsp;inches in the late 1880s and early 1890s. However, British-designed quickfiring ("QF" in British terminology, which became synonymous with charges in metal cartridge cases) continued to use screw breech blocks, but with their function merely to lock the cartridge in place rather than provide obturation. The powerful backward force generated by 6-inch QF guns still required a strongly seated breech screw with as much thread as possible. However, a basic interrupted-thread screw sufficiently long enough to have enough thread to secure the cartridge on firing still required three separate motions to operate – rotate, withdraw, swing aside after firing, and repeated in reverse before firing.

[[File:QF 6 inch gun coned breech screw.jpg|thumb|left|[[Elswick Ordnance Company|Elswick]] coned interrupted screw breech of [[QF 6 inch /40 naval gun|QF 6-inch naval gun]].]]
[[Elswick Ordnance Company]] (Armstrong's ordnance arm) developed a coned version of the interrupted-thread screw, with a decreasing rather than constant diameter towards the front. This eliminated the second "withdrawal" motion, with just two motions now necessary, rotate and swing aside. This proved short-lived, with Britain adopting charges in bags using the Welin stepped interrupted screw for all guns {{convert|5|in|abbr=on}} and up within several years of it becoming available.

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==See also==
* [[Armstrong Gun]]
* [[Anglo-German naval arms race]]

== References ==

{{refs}}

== External links ==

* [https://web.archive.org/web/20130208103234/http://riv.co.nz/rnza/hist/ord/breech.htm Royal New Zealand Artillery Association, Breech Mechanisms]
* [https://web.archive.org/web/20150121235504/http://www.riv.co.nz/rnza/hist/gun/rifled13.htm W. L. Ruffell, The Gun – Rifled Ordnance Breech Mechanisms]
* [https://archive.org/details/textbookordnanc00acadgoog Willian F Fullam & Thomas C Hart, USN, Text-Book of Ordnance and Gunnery. Chapter IV Breech Mechanisms] published by United States Naval Institute, Annapolis MD, 1905

[[Category:Artillery by type]]