List of British ordnance terms


List of British ordnance terms

This article explains terms used to describe the British Armed Forces' ordnance (i.e.: weapons and ammunition) used in World War I and World War II. Note that the terms may have slightly different meanings in the military of other countries.

BD

BD stands for "Between Decks" and applies to a naval gun mounting in which part of the rotating mass is below the deck, and part of it is above the deck. This allows for a lower profile of turret, meaning that turrets need not be superfiring (i.e. they can be mounted on the same deck and not obstruct each other at high angles of elevation.)

BL

BL, in its general sense, stood for breech loading, and contrasted with Muzzle Loading. The shell was loaded via the breech followed by the propellant charge.

BL in its formal British ordnance sense served to identify the gun as of the type in which the breech mechanism was responsible for "obturation" i.e. sealing the chamber [http://riv.co.nz/rnza/hist/ord/breech.htm Royal New Zealand Artillery Old Comrades Association, Breech Mechanisms] ] . For British guns this was a Crossley pad with an interrupted thread screw block eg a Welin screw. The shell was loaded via the breech, followed by the propellant charge in a cloth bag. A single-use "Vent Sealing Tube", a type of primer not dissimilar in appearance to a blank rifle round, was inserted into the breech for firing the gun.

It contrasts with QF. For instance, Britain before World War I had both QF and BL 6 inch guns. Both were "breech loading" in the general sense, but in the formal nomenclature it separated 6 inch guns with breeches designed for charges in brass cartridge cases from those designed for cloth bag charges.

Shells designed for one type were not necessarily suitable for use in the other type : for instance, a BL shell relied upon the tight fit of its driving band in the gun bore to prevent it slipping back when the gun was elevated, but a QF shell could rely upon the cartridge case, either fixed or separate, to prevent it slipping back. This may present difficulties for BL guns at high angles. A special cartridge was developed for BL 9.2 inch guns on H.A. mountings, with provision for a wooden (beech) stick to be inserted through the centre to prevent the shell slipping back on elevation. [Treatise on Ammunition 10th Edition 1915, Page 77]

BLC

BLC stood for "BL converted" and described a breech and breech mechanism modified from an early long-screw 3 or 4-motion to modern short-screw single-motion [http://riv.co.nz/rnza/hist/gun/rifled13.htm W L Ruffell, Breech Mechanisms] ] . An example is the conversion of the BL 15 pounder to BLC 15 pounder.

C.R.H.

Calibre Radius Head. Roughly, it describes the radius of a circle with the curve of the shell's nose on its circumference, expressed in terms of the shell's calibre. The longer and more pointed (and hence streamlined) the shell's nose, the higher the C.R.H. Typical c.r.h. for British shells leading up to World War I was 2 : e.g. the curve of the nose of a 2 c.r.h. 6-inch shell was equivalent to the curve of a circle with a radius of 12 inches. Shells of 4 c.r.h. were soon developed in WWI, identified by A following the shell mark number, B for 6 c.r.h. and so on. For modern streamlined shells post-WWI, 2 numbers were necessary to more correctly describe a shell's c.r.h. characteristics. For instance, the WWI 6 inch 26 cwt howitzer shell was 2 c.r.h., the WWII Mk 2D shell was correctly described as "5/10 c.r.h.". Detailed explanations are found at [http://www.navweaps.com/index_tech/tech-094.htm] and [http://members.tripod.com/~nigelef/ammo.htm#PROJECTILES] .

Cartridge

"Cartridge" has been used in different senses for British ammunition terminology. It typically describes the physical object containing the propellant that a gunner loads :-
*For S.A. (small arms) or Fixed QF artillery ammunition such as .303 or 18 pounder, this denoted the complete round, i.e. cartridge case, percussion cap or primer, propellant charge and projectile. [Treatise on Ammunition 1915, Pages 394, 531] In this use it is synonymous with "Round".
*For Separate QF artillery, Cartridge referred to the Cartridge case, its Primer, propellant charge, and the disposable lid and fastener of the case. [Treatise on Ammunition 1915, Page 440]
*In BL artillery terminology, Cartridge referred to the propellant unit only - there was no case. British cartridges consisted of sticks of Cordite bound up together with an igniter pad if necessary, in a cloth bag, usually silk. The "stick" nature of cordite gave the cartridges a degree of rigidity and hence they retained a tubular shape and could be handled and loaded as a solid unit even without a case. With BL, cordite is contained in 1 or more cloth bags joined together. The complete unit is termed a cartridge. The empty bag was termed an "empty cartridge". [Treatise on Ammunition 1915, Page 60.]

Heavy naval guns may require up to (e.g.) four separate cartridges to be loaded, each consisting of a ¼ charge to make up the full service charge.

Howitzer cartridges, both BL and separate QF, contained a central core of cordite surrounded by several stacked bags in the shape of rings, containing cordite. To obtain the appropriate "Charge" for the required range and angle of elevation, the gunner removed and discarded 1 or more rings before loading.

See Charge for how QF 25 pounder charge was varied in World War II.

Cartridge Case

The case, usually brass, holding the propellant charge. Used with Small arms and QF artillery ammunition. QF cases in 1915 could be cleaned and then reloaded up to a maximum of 6 firings with Cordite charges, with the record detailing the "Life of the Case" marked on the base. The limit was imposed by the fact that the case expanded on firing and had to be "rectified" by turning metal off the lower part to regain the correct dimensions. This weakened the case. [Treatise on Ammunition 1915, Page 393-394]

Charge

"Charge" was a concept or category label rather than a specific item. It can be described as "the standard amount of propellant specified to carry out a particular mission" :-
*Full Service Charge : the full amount of propellant intended for use in action at maximum range, for the usual shell. If a gun had e.g. a "heavy" and a "light" shell, there would be a separate Charge associated with the Heavy and Light shell.
*Reduced Service Charge : For practice or firing Star Shells (which were lighter than the normal shell).
*Proof charge : A charge giving 25% greater chamber pressure than the full service charge, intended only for the "proof" or testing of a gun. [Treatise on Ammunition 1915, Page 62]
*Blank Charge : Intending for firing without a projectile, usually a reduced charge.For practical purposes, specific Cartridges were specified for use to obtain the required Charge. A gunner dealt with cartridges and would know that he could load Cartridge X or Y for a full service charge for his gun, and Cartridge Z to fire a Star shell. Cartridges were sometimes made up of fractions of charges e.g. a 6 inch gun cartridge may be made up of 2 x 1/2 Charges or 1 x 2/5 and 1 x 3/5 Charge laced together. A gun normally fired all rounds using the full charge, and varied the range by elevating or depressing the barrel.

A howitzer gunner's job was more complicated because the range table would specify different "charges", or fractions of the full service charge, for different ranges and angles of shell descent. The standard cartridge for his gun which as a whole made up the full service charge, would consist of a central "mushroom" Cordite core and several smaller Cordite rings in bags stacked around the core, all tied together. It was designed so that 1 or more rings could be quickly removed and discarded before loading, hence providing progressively smaller charges. [Treatise on Ammunition 1915, Page 95] E.g. if the gunner was ordered to load Charge "X" he would know he had to remove the 2 top rings from the cartridge. This was the standard procedure for howitzers up to and including World War II.

In World War II a different system was introduced for varying charges for the QF 25 pounder gun-howitzer, which used separate-loading QF ammunition. A separate 2.7 lb "super charge" cartridge was available for firing the 20-pound high-velocity anti-tank AP shot, and an additional 4.5oz "super charge increment" could be added to that for even higher velocity. The cartridge for firing the standard 25-pound shell came ready-loaded with a red bag at the bottom containing the basic charge (Charge 1), together with white and blue bags laid lengthwise, as in a conventional gun charge, to make up the full service charge (Charge 3). The blue and white bags could be removed to provide progressively reduced charges (Charge 2 and Charge 1). From 1944 1 or 2 4oz "intermediate charge increments" could be added to the standard charge (replacing the blue bag) for high-angle fire and to provide greater control over angle of shell descent. [See [http://members.tripod.com/~nigelef/25pdrsheet.htm Nigel F Evans's website] for detailed explanation of 25 pounder charges]

For small arms or fixed QF ammunition, where the charge could not be varied by the gunner, the term Charge was used to identify the Cordite propellant within the cartridge case, and the round as a whole was referred to as Full or Reduced charge. E.g. an 18 pounder Star round consisted of a cartridge case containing a Reduced charge, and an attached Star shell.

Common Pointed

Common Pointed shell, or C.P. were a type of Common Shell used in naval service from the 1890s - 1910s which had a solid nose and a percussion fuze in the base rather than the Common shell's nose fuze. The ogival 2 c.r.h. solid pointed nose was considered suitable for attacking shipping but was not armour-piercing - the main function was still explosive. They were of cast or forged (3 and 6 pounder) steel and contained a gunpowder bursting charge slightly smaller than that of a Common Shell, a tradeoff for the longer heavier nose.Treatise on Ammunition 1915, Page 161.]

Common Shell

"Common shell" designated early British explosive shells filled with "low explosives" such as "P Mixture" (gunpowder) and usually with fuzes in the nose. Common shells on bursting (they did not "detonate") tended to break into relatively large fragments which continued along the shell's trajectory rather than laterally. They had some incendiary effect. As at 1914, Common shells 6 inch and up were of cast steel, smaller shells were of forged steel for service and cast iron for practice.Treatise on Ammunition 1915, Pages 158, 159, 198.] They were replaced by "Common Lyddite" shells in the late 1890s but some stocks remained as late as 1914.

Common Lyddite

British explosive shells filled with Lyddite were initially designated "Common Lyddite" and beginning in 1896 were the first British generation of modern "high explosive" shells. Lyddite is Picric Acid fused at 280°F and allowed to solidify, producing a much denser dark yellow form which is not affected by moisture and is easier to detonate than the liquid form. Its French equivalent was "Melinite". Common Lyddite shells "detonated" and fragmented into small pieces in all directions, with no incendiary effect. For maximum destructive effect the explosion needed to be delayed until the shell had penetrated its target.

Early shells had walls of the same thickness for the whole length, later shells had walls thicker at the base and thinning towards the nose. This was found to give greater strength and provide more space for explosive. Treatise on Ammunition 1915,. Pages 37, 158, 159, 198.] Later shells had 4 c.r. heads, more pointed and hence streamlined than earlier 2 c.r.h. designs.

Proper detonation of a Lyddite shell would show black to grey smoke, or white from the steam of a water detonation. Yellow smoke indicated simple explosion rather than detonation, and failure to reliably detonate was a problem with Lyddite, especially in its earlier usage. To improve the detonation "exploders" with a a small quantity of Picric powder or even of TNT (in smaller shells, 3 pdr, 12 pdr - 4.7 inch) was loaded between the fuze and the main Lyddite filling. Another difficulty of Lyddite was that it reacted dangerously with metal bases, which required that the interior of shells had to be varnished, the exterior had to be painted with leadless paint and the fuze-hole had to be made of a leadless alloy. Fuzes containing any lead could not be used with it.

When World War I began Britain was replacing Lyddite with modern "high explosive" (HE) such as TNT. After World War I the term "Common Lyddite" was dropped, and remaining stocks of Lyddite-filled shells were referred to as H.E. (or High Explosive) Shell Filled Lyddite. Hence "Common" faded from use, replaced by "HE" as the explosive shell designation.

For Shellite, a derivative of Lyddite, see HE below.

CP

CP stands for "Central Pivot" and was applied to a naval gun mounting that rotates around a central pivot that could be bolted to the deck without any structural alterations being required.

DCT

The "Director Control Tower" was a feature of naval ships. It was a trainable turret incorporating the gunnery officers, gun laying sights and a rangefinder. From here the gunnery officer could select targets and take the range, bearing and rates of change. This data would be provided to the Transmitting Station (TS), where a firing solution would be calculated and passed on to the gun turrets as the correct degree of training and elevation.

Gunpowder

Britain employed gunpowder as a propellant (before Cordite) and explosive filling under the following designations : [Treatise on Ammunition, 10th Edition 1915, Pages 4-9]
*E.X.E. : Propellant
*L.G. : Large grain : propellant
*Mealed powder : powder in fine dust form : used to ignite fuzes, friction tubes.
*Prism or Molded powders : Propellant pressed into regular hexagonal prism shape, with a hole in the centre to give even burning : included Prism Brown and Prism Black.
*Pebble powder : Propellant in cube shape
*P Mixture : Mixture of Pebble & Fine Grain powders : Explosive : filled Common & Common-pointed shells.
*Q.F. Mixture : explosive : filled medium sized common & common-pointed shells
*R.F.G.² : Rifle Fine Grain : dogwood charred for 8 hours : filling for Shrapnel & Star shells
*R.L.G. : Rifle Large Grain : Propellant; explosive filling for Armour-piercing shells
*S.B.C. Slow-Burning Cocoa : propellant, brown powder (cocoa refers to the colour).
*S.P. Small Pebble : Propellant

HA

"High Angle", a naval designation, equivalent to AA (anti aircraft), for a gun mounting which was capable of an elevation exceeding 50° from the horizontal, therefore allowing the gun to be used against aircraft.

HA/LA

"High Angle / Low Angle", a naval designation, equivalent to "dual purpose", for a weapon intended for engaging surface and airborne targets, and which therefore was on a mounting capable of elevating above 50 degrees but also effective at low elevations. Typical examples were the QF 4 inch Mk V of World War I, and QF 4 inch Mk XVI and QF 5.25 inch Mk I in World War II.

HE

"HE" in British terminology initially designated only shells filled with modern "high explosive" such as Trotyl (the British term for TNT), which was being introduced when World War I began, and Amatol from 1915. It contrasted with Common Shell, which were filled with older explosives such as gunpowder, and Common Lyddite, the earlier British high explosive shell. Britain first used pure TNT from late 1914, but this proved expensive and difficult to manufacture in the necessary large quantities, and was also inefficient as much energy was output as heavy black smoke. Amatol, a mixture of cheap Ammonium Nitrate and TNT (typically "60/40" : 60% ammonium nitrate and 40% TNT for shells; or even 80/20 for mortar bombs) proved almost as effective as pure TNT and was soon adopted as the preferred HE filling in WWI. TNT and Amatol were approximately 20% less sensitive to shock and hence safer than Lyddite.

After World War I, remaining stocks of Lyddite-filled shells were redesignated "H.E. Shell Filled Lyddite", and henceforth the term H.E. encompassed all Lyddite, TNT and subsequent high-explosive shell types.

From 1919 into the 1930s a less sensitive and safer version of Lyddite named Shellite, consisting of 70% Lyddite and 30% dinitrophenol was used in naval AP shells. [Tony DiGiulian, [http://www.navweaps.com/Weapons/Gun_Data_p2.htm Definitions and Information about Naval Guns Part 2 - Ammunition, Fuzes and Projectiles] ]

Amatol continued in use to 1945 [I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914-1918. Ian Allan publisher, London, 1972, Page 215] when it began to be replaced by a 60/40 mixture of RDX and TNT.

LA

"Low Angle", a naval designation for a gun mounting not capable of high angles of elevation, and intended solely for firing at surface targets. In theory any CP mounting was an LA mounting by default.

ML

ML was "muzzle-loading". By World War II, there were no more muzzle-loaded guns in British use, so ML meant mortars, as the 'bomb' was dropped tail-first down the barrel from the muzzle. See mortar for more information.

Ordnance

In British use, Ordnance meant a specific barrel and breech e.g. "Ordnance QF 18 pdr gun Mk II" referred to the Mk II barrel and breech of the QF 18 pounder gun. The ordnance by itself, i.e. without a carriage, was useless, and hence the full designation of a deployable gun, known as an Equipment, might be Ordnance QF 18 pdr gun Mk II on carriage, field, QF 18 pdr gun Mk I.

P

P refers to a "pedestal" mounting for a gun, and was used by the Royal Navy. It differed from a Central Pivot mounting in that the mounting rotated around a fixed pedestal, rather than being bolted directly to the deck.

QF

QF came from "Quick-firing". The designation was put into use in late 19th century in two different meanings. In naval terms it was first used to describe small guns firing fixed ammunition i.e. a complete round formed from a metal (brass) cartridge case containing the propellant and projectile in one unit thus enabling higher firing rates. An early example was the QF 6 pounder Hotchkiss. In later pieces, the charge was sometimes separated from the shell to reduce the individual weight of loading, but the charge remained in a brass case, rather than a Clarkson case or canvas bag.

In formal British ordnance terminology the term QF came to mean that the propellant charge is loaded in a metal, usually brass, case which provides obturation i.e. seals the breech to prevent escape of the expanding propellant gas. The term QF hence described both the breech-sealing mechanism and method of loading propellant charges. Ordnance of other countries employed other techniques, and hence this description and distinction is limited to British ordnance.

Fixed QF

In lighter QF guns, including field guns and anti-aircraft guns, the round was complete : "Fixed Ammunition", where the shell was attached to the cartridge case. Examples are QF 3 pounder Vickers, QF 18 pounder field gun, QF 4 inch Mk V anti-aircraft gun. Fixed QF was suited for rapid loading, especially at high angles, and was limited by the total weight of cartridge and projectile, which had to be easily handled by one man.

eparate QF

In other guns, typically naval guns 3 inches or above such as the QF 12 pounder 12 cwt and QF 6 inch naval gun and howitzers such as the QF 4.5 inch Howitzer and Ordnance QF 25 pounder gun-howitzer, the projectile was loaded separately to the cartridge case containing the propellant : "Separate Ammunition". This system was suitable for howitzers as it allowed the gunner to remove part of the cordite charge before loading if required for shorter ranges. Separating the cartridge and projectile also allowed the weight of loading to be be shared by two men.

Characteristics

In all types, the primer for the round was in the cartridge case base. The term QF hence effectively describes the breech sealing mechanism, allowing a sliding block, which can generally be operated faster than a BL mechanism, and is characteristic of small to medium artillery. Early QF guns offered the advantage over BL guns that no time was wasted in inserting vent tubes after loading, as the primer was built into the case, and sponging out of the chamber was not necessary between rounds. QF also removed the risk of back-flash.Treatise on Ammunition 1915, Page 393] QF also, by rigidly fixing the position of the primer, igniter and cordite charge in the case relative to each other, improved the chances of successful firing compared to BL with its flexible bags.

By the early 1900s Bitish doctrine held that QF ammunition, while allowing faster-operating breeches, had the disadvantage that ammunition is heavier and takes up more space, which was limited on warships. For guns larger than 6 inches it becomes impractical as the cartridge case becomes unwieldy for manual operation, and it does not allow charges to be loaded via multiple bags as BL does. Also, dealing with misfires was simpler with BL, as another tube could simply be tried. With QF the gunner had to wait a time and then open the breech, remove the faulty cartridge and reload. Already by 1900, modern BL breeches allowed the gunners to insert vent tubes while the gun was being loaded, obviating one of the previous QF advantages, and hence the Royal Navy abandoned the QF 6 inch gun and returned to BL 6 inch guns with the Mk VII.Treatise on Ammunition 1915, Page 393]

Another potential disadvantage associated with QF came with the horizontal sliding block breech, as used with the QF 4.5 inch Howitzer. With the gun traversed at high elevation, the block could not be operated as it came into contact with the inside of the box carriage. Not all British QF guns in fact used sliding blocks - the QF 2.95 inch and QF 3.7 inch mountain guns and the QF 18 pounder used screw breeches. The thing to note is that their screw mechanism were much lighter and simpler than BL screw mechanisms and served merely to lock the cartridge in place.

It is worth noting that British artillery doctrine considered QF, even separate-loading, as unsuited for guns over 5 inches following its experience with the QF 6 inch in the 1890s, while European militaries such as Germany continued to use separate QF with sliding-block breeches for large guns up to 12 inches.

In loose colloquial use the term Quick Firing has been used to describe modern artillery having attributes such as recoil buffers and quick shell loading characteristics, dating from the late 19th century.

QF SA

QF SA stood for "Quick Firing, Semi Automatic" and applied to naval QF guns where there was a mechanism to automatically open the breech and eject the case after firing. This was useful to enable a high rate of fire. An example was the QF 3 inch 20 cwt anti-aircraft gun.

RBL

"Rifled Breech Loading". Refers to the first generation of British Armstrong rifled breech loading guns in the 1860s, and differentiates these from the second unrelated generation of rifled breech loaders beginning in the 1880s which are referred to simply as BL. The "RBL" guns were considered to be failures and Britain reverted to RML guns from 1870 to 1880.

Recuperator

"Recuperator" was the British name for the mechanism which returned the gun barrel to its firing position after recoil. US ordnance uses the term "run-out cylinder".

Hydro-spring

guns, all dating from 1904-5, where the oil, pistons and springs were integrated in a tubular housing above the barrel. This configuration made the entire recoil system vulnerable to enemy gunfire, and it was protected to some extent in the field by being wound with thick rope. Other guns had the pistons and springs in separate housings. Note that "hydro-" here is a misnomer : oil was the liquid used, not water.

Hydro-pneumatic

Both the Army and Navy were in the process of introducing a "hydro-pneumatic" recoil system when World War I began, in which the recuperators were driven by air compression rather than springs. Examples were the navy's new QF 4 inch Mk V gun and the army's new BL 9.2 inch howitzer.The unanticipatedly heavy rates of fire experienced (mainly on the Western front) early in World War I caused many spring breakages in the 1904 generation field artillery (including in the Mk I 60 pounders at Gallipoli) and led to field modification to the 18 pounder which replaced the springs in the housing above the barrel with a pneumatic unit. By the end of the war the hydro-pneumatic system had become standard for a new generation of field artillery, typically seen in a box-shaped unit below the barrel in the 18 pounder Mk IV, 60 pounder Mk II, 6 and 8 inch howitzers and 6 inch Mk 19 gun.

RML

"Rifled Muzzle Loading" : the barrel had grooves into which "studs" on the shell fitted, to spin the shell and hence improve accuracy and range. Both the shell and propellant charge are loaded through the muzzle. "RML" became necessary to disambiguate new rifled and old un-rifled muzzle loaders (ML) beginning in the late 1850s. Modern examples are rifled field mortars. The last recorded deployment of British RML guns was some RML 2.5 inch Mountain Guns in German East Africa in 1916.

Round

The complete set of components needed to fire the gun once. Consists of a Projectile, a propellant Cartridge and Primer or Igniter Tube. A Fixed Round had all the components integrated into a brass cartridge case with the projectile attached. A Separate round required the projectile and propellant Cartridge (either in bags or brass Case) to be loaded separately.

RPC

RPC stands for "Remote Power Control". This is where a gun turret automatically trains and elevates to follow the target being tracked by the DCT (see above). Mountings would also have local control in the event of the RPC or director tower being disabled.

.B.C.

Slow Burning Cocoa Powder. A form of Brown Prismatic Powder, i.e. gunpowder, with more charcoal, saltpetre and moisture but less sulphur than black powder. Cocoa referred to the appearance rather than composition. Used for early large long-barreled guns, where its slow-burning properties gave the projectile a prolonged smooth acceleration instead of the short violent accereration typical of black powder. Was inefficient as most energy was expended as smoke. Required a primer of black powder to ignite.

BML

SBML stands for "Smooth Bore Muzzle Loading". The barrel is not rifled and the projectile is loaded via the muzzle of the barrel. All early cannons were of this type. Modern examples of this type of weapon are fin-stabilised light field mortars, in which the mortar bomb is dropped into the mortar barrel for firing and spin and stability is imparted via fins.

teel Shell

"Steel Shell" (with capitals) was the British term used to describe the Hotchkiss 3 and 6 pounder Common pointed shells. They had attributes of British "Common Pointed" shells as they were filled with gunpowder, had base pecussion fuzes and a heavy pointed nose (almost 3 c.r.h.). But the nose was closer in design to British A.P. shells - the solid section was longer than Common Pointed, and the body held proportionately less powder than Common Pointed. It was intended for Naval use.

In common usage, "steel shell" (without capitals) served to differentiate a shell constructed of steel from one constructed of cast iron (C.I.).

Tube

See Vent-Sealing Tube

UD

UD stands for "Upper Deck", and describes a naval gun mounting in which the rotating mass of the turret is mounted above the deck, with usually only the ammunition feed trunking piercing the deck.

Velvril

"Velvril paint" was used to line larger common shells to prevent the gunpowder filling from coming into contact with the iron or steel shell wall. This was both to avoid the saltpetre from causing corrosion in the presence of any moisture, and also provided a smooth surface that prevented friction between the gunpowder and shell wall, hence reducing the risk of spontaneous ignition when the shell was fired. It was made up of 24 parts zinc oxide, 3.5 yellow ochre, 0.5 red iron oxide, 15 nitrated castor oil, 7.5 nitro-cellulose of very low nitration, 60 acetone oil.

Vent-Sealing Tube

Usually abbreviated to "V.S. tube" or just Tube. This was the traditional, reliable British method of fully igniting powder charges in BL guns to fire projectiles, especially large shells. Briefly, after the powder cartridge was loaded (or even during the loading process), the tube was inserted through a vent in the breech. Vents were either "radial" i.e. at right-angles to the barrel length, bored through the top of the barrel into the chamber; or "axial" through the centre of the breech mechanism and "mushroom" into the chamber. When the breech was closed, one of several methods was then used to trigger the tube, which then sent a powerful flash into the breech. The flash ignited a special "igniter" material in the end of the cartridge, and the igniter in turn ignited the main propellant charge (some form of Cordite). A powerful reliable flash from the tube was required because with bag charges, especially in the stress of combat and/or with variable howitzer charges, it could not be guaranteed that the igniter in the cartridge would be up close to the vent - it may have been pushed in too far, leaving a gap. The Tube was designed to expand on ignition and seal the vent, preventing escape of gas. Tube types :-
*Percussion tube - the tube was inserted in an axial vent in the breech and triggered by a firing pin in a percussion lock in the breech. Single-use. Used with medium-heavy guns and howitzers, e.g. 60 pounder Gun.
*Electric tube - the tube was fired by an electric current from mains or battery. Considered safe, but cumbersome for field use. Common with naval and coast defence guns.
*Friction tube - The tube would have a lanyard attached, with length proportional to the size of the gun, which when pulled caused friction inside the tube which ignited a powder charge, much like striking a match. Single-use. Originally of "Copper" and "Quill" types, replaced by the "T" tube by late 1890s. They were used in great quantitities by field artillery and will be found on old British battlefields up to 1904, e.g. in South Africa. They were inserted in a "radial" vent on top of the breech, such as with the BL 15 pounder. The T design, with the friction wire to which the lanyard was attached running through the crosspiece of the T, ensured that when the lanyard was pulled and the gun recoiled the wire was pulled smoothly out of the T piece without exerting force on the vertical part of the T and hence affecting the gas seal. From 1904, the new generation of field artillery was QF with propellant in brass cases with self-contained percussion primers, while small naval QF cases had self-contained electric primers. Hence from then onwards tubes were only used for guns of 60 pounder (5 inch) and upwards, usually Percussion tubes; and for a few small BL guns such as the 2.75 inch mountain gun, usually Friction tubes. However, Britain entered WWI with many old BLC 15 pounders which continued to require T Tubes until phased out by 1916. To approach a QF rate of fire they used a special "push" version of the T friction tube which was inserted into an axial vent in the breech like a BL percussion tube and fired by a similar mechanism to a firing pin activated by a lever rather than being pulled by a lanyard.

Tubes could also be used with QF cartridges fitted with tube adaptors in place of primers, as with the QF 12 pounder. [Treatise on Ammunition 1915, Pages 349-375]

Windage

"Windage" referred to the amount of propellant gas that escaped between the projectile's side and gun barrel on firing, and hence failed to contribute to accerating the projectile. Up to half of the gas was lost in this way in old smoothbore artillery. From 1859, Armstrong rifled guns used a lead coating on the shell to minimise windage and simultaneously to engage the rifling. Windage was effectively eliminated with the introduction of copper driving bands, with a diameter slightly larger than the bore. The elimination of windage necessitated a new design of timed fuze, because the burning propellant gas escaping past the head of the shell had been used to ignite the gunpowder timer train in the fuze in the shell nose. The new fuses used the shock of firing to ignite the timer.

Notes

References

*Treatise on Ammunition, 10th Edition 1915. War Office, UK. Facsimile reprint published by Imperial War Museum and Naval & Military Press, 2003.


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