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This article explains certain terms used for British ordnance during World War I and World War II.

Contents 1 BD 2 BL 3 CP 4 DCT 5 DP 6 HA 7 HA/LA 8 LA 9 ML 10 P 11 QF 12 QF SA 13 RML 14 RPC 15 UD

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 stood for "Breech Loading". The shell was loaded and then the propellant after in cloth bags. The breech mechanism was responsible for sealing the chamber. For British guns this was a Crossley pad with an interrupted thread screw block eg a Welin screw. A primer, not dissimilar in appearance to a blank rifle round, was inserted into the breech for firing the gun.

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.

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.

A "dual purpose gun" is a naval artillery mounting designed to engage both surface and air targets.

"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.

See also: Dual purpose gun

"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.

"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 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.

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 came from "Quick-firing". The designation was put into use in late 19th century in two different meanings. In naval terms it was used to describe 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. 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 field artillery the term 'Quick-Firing' means that the gun is fitted with a recoil system that eliminates the need to lay the gun between shots fired. In some guns the round was complete; in others such as the QF 25 pounder gun-howitzer the shell was loaded separately to the cartridge case containing the propellant. The primer for the round was in the cartridge base. Thus, excluding naval artillery, the term 'Quick-Firing' has got nothing to do with the ammunition.

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.

"Rifled Muzzle Loading", a term in use with the advent of rifled artillery, but before the universal adoption of breech loading. As there were no smooth-bore breech loaders, BML was not a required term, but RML was necessary to disambiguate rifled and un-rifled muzzle loaders.

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.

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.