Glossary of British ordnance terms

Between decks: 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 for a turret, meaning that the 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== The term BL, in its general sense, stood for breech loading, and contrasted with muzzle loading. The shell was loaded via the breech (i.e. the gunner's end of the barrel, which opened) followed by the propellant charge, and the breech mechanism was closed to seal the chamber. Breech loading, in its formal British ordnance sense, served to identify the gun as the type of rifled breechloading gun for which the powder charge was loaded in a silk or cloth bag and the breech mechanism was responsible for "obturation" i.e. sealing the chamber to prevent escape of the propellant gases. The term BL was first used to refer to the Armstrong breechloaders, introduced in 1859. Following the discontinuation of Armstrong breechloaders and the period of British rifled muzzle-loaders RML, British breechloaders were re-introduced in 1880. At this point the term rifled breech-loaders RBL was retrospectively introduced to refer to the Armstrong breechloaders, which had a totally different breech mechanism, and since then the term breech-loaders BL has applied exclusively to the type of breechloader introduced from 1880 onwards, using an interrupted-screw breeches. Early British Elswick breechloaders in the 1880s used a steel "cup" obturation method. This was quickly superseded in guns designed by the Royal Gun Factory by the French de Bange method, the basic principle of which is still in use today. In British service this became a Crossley pad with an interrupted thread screw block e.g. 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. While originally, the term "BL" contrasted with "ML", or "muzzleloader" guns, after muzzleloaders were discontinued, the term came to distinguish between traditional, non-obturating guns with fabric propellant bags and separately loaded shells, and quick-firing QF guns which used self-sealing brass cartridge cases, and which usually had the propellant and projectile fixed together as a unit for faster handling and loading. For instance, Britain before World War I had both QF and BL guns. Both were "breech loading" in the general sense, but in the formal nomenclature it separated guns with breeches designed for charges in brass cartridge cases for quick-firing QF from those designed for cloth bag charges for breech-loaders BL. 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 presented difficulties for BL guns at high angles. A special cartridge was developed for BL guns on HA mountings, with provision for a wooden (beech) stick to be inserted through the centre to prevent the shell slipping back on elevation. Although fixed ammunition allows for a rapid rate of fire in small to medium guns, BL is a better choice for heavy calibre guns; propellant was loaded in a number of small fabric bags, because a single bag holding the full charge would be far too big and bulky for the handlers to lift. Using fabric allows for the charge to be broken into small, easily handled units, while it would be difficult to design a system by which multiple small metallic-cased charges were loaded and fired at the same time. Using multiple small fabric bags also allows the gunners to use a reduced charge if need be. ==BLC==

The term "BLC" stood for "BL converted" and referred to a breech and breech mechanism modified from an early long-screw three- or four-motion to modern short-screw single-motion. An example is the conversion of the BL 15-pounder to BLC 15-pounder. ==C.R.H.==

Calibre radius head: 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 two: e.g. the curve of the nose of a two C.R.H. shell was equivalent to the curve of a circle with a radius of . Shells of four C.R.H. were soon developed in World War I, identified by an A following the shell mark number, B for six, and so on. For modern streamlined shells post-World War I, two numbers were necessary to more correctly denote a shell's C.R.H. characteristics. For instance, the World War I 6-inch 26 cwt howitzer shell was two C.R.H., and the World War II Mk 2D shell was referred to as "5/10 C.R.H.". ==Cartridge==

"Cartridge" in British ammunition terminology typically refers to the physical object containing the propellant that a gunner loads. For small arms and fixed QF artillery ammunition, e.g., the .303 or 18-pounder respectively, this denoted the complete round, that is, the cartridge case, percussion cap or primer, propellant charge and projectile. 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. In BL artillery terminology, cartridge referred to the propellant unit only – there was no case. British cartridges contained gunpowder until about 1892, and thereafter sticks of cordite bound 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 one or more cloth bags joined together. The complete unit is termed a cartridge. The empty bag was termed an "empty cartridge". Heavy naval guns may require up to four separate cartridges to be loaded, each consisting of a 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 ring-shaped bags of cordite. To obtain the appropriate "charge" for the required range and angle of elevation, the gunner discarded one or more rings before loading. See charge for how Ordnance QF 25-pounder charges varied in World War II. ==Cartridge case==

The case, usually brass, holding the propellant charge. Used with small arms and QF artillery ammunition. The QF cases in 1915 could be cleaned and then reloaded up to a maximum of six firings with Cordite charges, with the record detailing the "life of the case" marked on the base. The limitation on the number of firings was due to the case expanding on firing, having to be "rectified" by turning metal off the lower part, which restored the correct dimensions but progressively weakened the case. ==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 purpose": • 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 shells. • 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. • Blank charge: intended for firing without a projectile, usually a reduced charge. • Battering charge: a specially large charge for use with "Palliser" projectiles, which were an early British armour-piercing projectile of the mid-to-late 19th century. 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 (e.g.) 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 gun cartridge may be made up of two half charges or one two-fifths and one three-fifths 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 like doughnuts, all tied together. It was designed so that one or more rings could be quickly removed and discarded before loading, hence providing progressively smaller charges. E.g. if the gunner on a QF 4.5-inch howitzer was ordered to load charge four, he would know he had to remove the top ring from the cartridge, leaving four rings; for charge three he would remove two rings. Discarded rings were burned after the action. 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 "super charge" cartridge was available for firing the high-velocity anti-tank AP shot, and an additional "super charge increment" could be added to that for even higher velocity. The cartridge for firing the standard shell came ready-loaded with a red bag at the bottom containing the basic charge (charge one), together with white and blue bags laid lengthwise, as in a conventional gun charge, to make up the full service charge (charge three). The blue and white bags could be removed to provide progressively reduced charges (charge two and charge one). From 1944 one or two "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. 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 a 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 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 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", Japanese equivalent was "shimose". 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. 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 small quantity of picric powder or even of TNT (in smaller diameter shells, such as in 3-pounder and 12-pounder guns) was loaded between the fuze and the main lyddite filling or in a thin tube running through most of the shell's length. Lyddite presented a major safety problem because it reacted dangerously with metal bases. This 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 HE (high explosive) shell filled lyddite. Hence "common" faded from use, replaced by "HE" as the explosive shell designation. Common lyddite shells in British service were painted yellow, with a red ring behind the nose to indicate the shell had been filled. For shellite, a successor of lyddite, see HE below. ==Common pointed==

Common pointed shells, or CP were a type of common shell used in naval service from the 1890s to the 1910s which had a solid nose and a percussion fuze in the base rather than the common shell's nose fuze. The ogival two 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 (three- and six-pounder) steel and contained a gunpowder bursting charge slightly smaller than that of a common shell, a tradeoff for the longer heavier nose. In British service common pointed shells were typically painted black, except 12-pounder shells specific for QF guns which were painted lead colour to distinguish them from 12-pounder shells usable with both BL and QF guns. A red ring behind the nose indicated the shell was filled. By World War II they were superseded in Royal Navy service by common pointed capped (CPC) and semi-armour piercing (SAP), filled with TNT. ==Common shell==

"Common shell" is a designation for early 19th century British explosive shells filled with "low explosives" such as "P mixture" (gunpowder) and usually had the fuzes located 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. In the late 19th century "double common shells" were developed, lengthened so as to approach twice the standard shell weight, to carry more powder and hence increase explosive effect. They suffered from instability in flight and low velocity and were not widely used. As at 1914, common shells and larger were of cast steel, smaller shells were of forged steel for service, and cast iron for practice. They were replaced by "common lyddite" shells by the late 1890s, but some stocks remained as late as 1914. In British service common shells were typically painted black with red bands behind the noses to indicate the shells were filled. ==CP==

Central pivot: 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. == cwt ==

The abbreviation cwt stands for hundredweight, which, despite the name, is equal to , and signifies the weight of the gun barrel and breech. It is sometimes included in the name of a gun to differentiate it from other guns of the same calibre or weight of shot. For example, the QF 12-pounder 18 cwt naval gun is a different (and heavier) weapon than the QF 12-pounder 8-cwt Mk I naval gun, though they both fire shells of the same approximate weight (). ==DCT==

The director-control tower (DCT in British usage or "director" in US usage) was a feature of naval ships. It was a trainable turret incorporating the gun-laying sights and often 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. ==Effective full charge==

(Note: The British Army term is usually equivalent full charge) Gun barrels naturally experience internal wear when fired, caused by mechanical wear from the projectile moving along the barrel, and thermal and chemical wear from propellant gases. This wear can reduce muzzle velocity and hence range, affect accuracy, produce unstable projectile flight, and, eventually, cause the gun barrel to fail. Most guns are capable of firing different types of ammunition with varying charges, and not all of these combinations produce the same firing damage per round fired. The concept of ‘effective full charge’ provides a means of estimating the remaining life of a gun barrel taking into account the varying charges that can be fired from it before it becomes so worn as to be unusable, or no longer safe. To illustrate, the round (i.e. the combination of projectile and propelling charge) that produces the most firing damage is assigned an effective full charge (EFC) value of "one*. Other round combinations are assigned lesser values derived from testing and experience. If a gun barrel is capable of firing three different round types: round A (EFC = 1); round B (EFC = 0.75); and round C (EFC = 0.25), and if 100 of each round type is fired, then the barrel is said to have fired (100×1.00) + (100×0.75) + (100×0.25) = 200 EFCs. If it had previously been determined from testing and experience that this type of barrel has an estimated wear life of 250 EFCs, this specific barrel is at about 80% of its useful life. Plans would be made to order a replacement barrel within the time an additional 50 EFCs were expected to be fired. However the actual decision to retire any specific barrel would be made on examination and measurement of actual wear rather than that predicted by the EFC count. ==Equipment==

This was the term for a gun together with its gun carriage, i.e. the complete set of equipment needed to be able to fire the gun, as the gun could only be fired when mounted on its correct carriage. The carriage could be a wheeled carriage, a static siege carriage or include both a traversing mounting and railway wagon in the case of a railway gun. For example, a complete deployable gun might be described as "Ordnance QF 18 pdr gun Mk II on carriage, field, QF 18 pdr gun Mk I". ==Gunpowder==

Britain employed gunpowder as a propellant until superseded by Cordite Mk I from 1892, and as an explosive filling in common shells until slowly superseded by lyddite from the late 1890s. In World War I gunpowder was still in wide British use : • in shrapnel shells as a burster to propel the bullets out of the case • in "igniter pads" at the ends of cordite cartridges to facilitate ignition • as the delay mechanism in time fuzes for artillery • in vent tubes for firing guns. British gunpowder designations were : • E.X.E.: "extra experimental": propellant: mixture of brown and black powders, used with BL 6 inch guns Mk III, IV & VI • L.G.: large grain: propellant • Mealed powder: powder in fine dust form: used to ignite fuzes, friction tubes • Prism or moulded powders: propellant pressed into regular hexagonal prism shape, with a hole in the centre to give even burning: included prism brown" (slower burning) and "prism black" (faster burning) • P: Pebble powder: propellant in cube shape, designed to reduce the ratio of surface area to weight, and hence to slow the rate of burning to reduce strain on guns. A larger weight of P (approximately 16% more) is required than R.L.G. for an equivalent charge. • S.P.: propellant: P specially selected for consistency, for use in BL guns • P mixture: mixture of pebble and fine grain powders: explosive: filled common and common-pointed shells • Q.F. mixture: explosive: filled medium-sized common and common-pointed shells • R.F.G.: rifle fine grain: dogwood charred for eight hours: bursting charge for shrapnel and 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). ==Gas-check==

Attached to the base of RML artillery shells from 1878 onwards to avoid gas wastage on firing, and to rotate studless shells. It was an interim measure between studs and modern driving bands. Related terms: • "Attached gas-check" – used with studded ammunition • "Automatic gas-check" – used with studless ammunition • "Rotating gas-check" – synonymous with "automatic gas-check" (Note: The term "gas-check" was hyphenated in official British government publications of the late 19th and early 20th century. These publications also used the term "automatic gas-check" while acknowledging that the term "rotating gas-check" had been used previously. ==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, 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 both surface targets and aircraft, on a mounting capable of elevating above 50 degrees but also effective at low elevations. Typical examples were the QF 4-inch Mk XVI, QF 5.25-inch gun, and QF 4.5-inch gun used in World War II and later. ==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 shells, which were filled with older explosives such as gunpowder, and common lyddite, the earlier British high-explosive shell. Britain also used Tetryl before World War I under the designation "composition exploding" (C.E.). The HE shell filling was detonated by a fuze, usually augmented by a "gaine" to ensure complete ignition, causing the thick steel shell case to shatter into large and small fragments at great velocity in all directions. Britain first used pure TNT for land warfare shells 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 (initially "40/60": 40% ammonium nitrate and 60% TNT for land shells and 80/20 from 1917) proved 27% more powerful than pure TNT and was soon adopted as the preferred HE filling in World War I. TNT and Amatol were approximately 20% less sensitive to shock and hence safer than lyddite, and Amatol 80/20 cost only 7d per pound () to produce in 1917 compared to 1s 11d () for lyddite and 1s 3d () for TNT. Britain was slow to move from 40/60 Amatol to the preferred 80/20 mixture during World War I, due to manufacturing difficulties. The preferred method for filling explosive shells was by pouring the molten mixture through the fuze hole in the shell nose or base. This was well suited to Lyddite filling, but it was found that Amatol with more than 40% ammonium nitrate did not pour well. Hence it was not simply a case of switching existing filling machinery from Lyddite to Amatol. Dry filling with Amatol 80/20 in block form and by pressing was used but was not considered to be a success. By the end of World War I the process for pouring 80/20 Amatol as a shell filling for land warfare shells had finally been perfected and was in large–scale production. The Royal Navy resisted switching from Lyddite to Amatol for its shells because it considered Amatol was too hygroscopic (water-absorbing) to be suitable for use at sea, and instead used pure TNT as its high-explosive replacement for Lyddite. After World War I, remaining stocks of Lyddite-filled naval 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. Amatol continued in field use to 1945 when it began to be replaced by a 60/40 mixture of RDX and TNT. High-explosive shells were typically painted yellow in British service in World War I, with a red ring below the nose to indicate the shell was filled and a green ring round the body to indicate filling with TNT or Amatol. In World War II they were typically painted olive green. ==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== Muzzle-loading. By World War II, there were no muzzle loading artillery guns in British use, so ML was used only for mortars, as the mortar bomb was dropped tail-first down the barrel from the muzzle. ==Ordnance==