Royal Garrison Artillery

The Royal Garrison Artillery (RGA) was an arm of the Royal Artillery that was originally tasked with manning the guns of the British Empire's forts and fortresses, including coastal artillery batteries, the heavy gun batteries attached to each infantry division, and the guns of the siege artillery.

History
The Royal Garrison Artillery came into existence as a separate entity when existing coastal defence, mountain, siege and heavy batteries of the Royal Artillery were amalgamated into a new sub-branch. A royal warrant provided that from 1 June 1899: "'... the mounted and dismounted branches of the Royal Regiment of Artillery shall be separated into two corps... to be named respectively (a) the Royal Horse Artillery and the Royal Field Artillery: (b) the Royal Garrison Artillery.'"

The Royal Regiment of Artillery, thenceforth, was divided into four branches. Other than mounted or unmounted dress, the obvious distinction in uniform was by the shoulder title badges: RGA; RFA; RHA; and RA (for the branch tasked with managing ammunition dumps and supply to units in the field).

The RGA retained the badge and dress uniform (dark blue with scarlet facings) of the Royal Regiment of Artillery, but personnel were normally clothed and equipped as dismounted men. After 1920 all RGA personnel were classified as mounted men, whether serving in horse-drawn, mountain or tractor-drawn batteries,

From 1914 when the army possessed very little heavy artillery, the RGA grew into a very large component of the British forces on the battlefield, being armed with heavy, large-calibre guns and howitzers that were positioned some way behind the front line and had immense destructive power. The corps name was discontinued in 1924, when the RGA was re-amalgamated into the Royal Artillery.

Pre-World War I mobile artillery tactics
Prior to the First World War artillery would manoeuvre on the battlefield beside the infantry and cavalry. The field artillery would form part of a battle line alongside the infantry and, on occasion, the horse artillery would charge alongside the cavalry with guns, limbers and caissons and all.

Use of fixed artillery
Fixed artillery (that which is not meant to move, other than for the purpose of aiming) was placed in forts and batteries in locations where they might protect potential targets (ports, cities, etc.) from attack, or from where they might prevent the advance of an enemy. This included forts and batteries intended to protect against military forces on the land, and against naval forces on the sea. Coastal artillery relied primarily on high velocity guns, capable of striking out at ships at a great distance, and penetrating their armour. Inland defensive batteries might have armament better suiting use against personnel. Mobile (field) artillery pieces were sometimes used that could be quickly re-deployed as required between fortifications that were not permanently manned or armed. Fixed batteries were operated, in the late 19th and early 20th Centuries, by the RGA and Militia Artillery reservists (often with support from other units, such as engineers operating searchlights for night-time firing).

Conventional wisdom held that a naval force would need a three-to-one advantage over coastal artillery, as the land-based artillery had the advantage of firing from a fixed platform, with resultant advantages in accuracy, especially as range increased. By the start of the 20th century, the increasing size of the capital ships of the world's largest navies, and of the guns they wielded, was already sounding the death knell of coastal artillery. As the primary armament of battleships and battle-cruisers reached 16 inches, while coastal artillery was typically 6 inch or 9 inch guns, a large naval force, including capital ships, could level coastal batteries from a range that kept them out of reach of answering fire. The advent of artillery had changed the design of fortifications centuries before, spelling the end of high-walled castles.

By the 20th century, fortifications were being designed with as much surrounding embankment by earthworks as possible. While this provided some protection from direct fire, it made defense against infantry more difficult, and did nothing to protect from high trajectory fire landing from above, or from air-bursting explosive shells, which rained the area enclosed by walls with shrapnel. In Bermuda, in the latter part of the 19th Century, where the War Office had expended vast fortunes building up fortifications to protect the Royal Naval Dockyard, it was decided belatedly that the Dockyard's own fleet of naval vessels could provide a more effective defence. With the advent of the aeroplane, and the missile, fixed artillery was both superseded and too vulnerable to continue in use. The last coastal artillery was removed from use in the 1950s.

First World War
With the new long-range small arms available to the infantry in the era before World War I, artillery fighting in the infantry line was increasingly brought under fire. The solution to this was the principle of standing off and engaging the enemy with indirect fire. However, even after this became official military doctrine, field and horse artillery on both sides kept trying to fight in the old way. One instance was a gun duel fought between British and German horse artillery units using open sights during the Retreat to the Marne. In the quagmire of trench warfare that followed it was finally realised that it was not the place for the artillery to be in the infantry line.

Henceforth the artillery would be positioned well behind the infantry battle line, firing at unseen targets, at co-ordinates on a map calculated with geometry and mathematics. As the war developed, the heavy artillery and the techniques of long-range artillery were massively developed. The RGA was often supported by the Royal Flying Corps (RFC) who had devised a system where pilots could use wireless telegraphy to help the artillery hit specific targets. The RFC aircraft carried a wireless set and a map and after identifying the position of an enemy target the pilot was able to transmit messages such as A5, B3, etc. in morse code to a RFC land station attached to a heavy artillery units, such as Royal Garrison Artillery Siege Batteries.

The Siege batteries (such as 9th Siege Battery at the Battle of the Somme) had the largest guns and howitzers; mounted on railways or on fixed concrete emplacements.

Ammunition supply to the Royal Field Artillery (RFA) and other field artillery units was normally the role of the Royal Artillery: that part of the Royal Regiment of Artillery which retained the Royal Artillery (RA) shoulder badges. However during the war the RGA, which had large numbers of men idling in fortified batteries around the World with little chance of seeing action, provided a draft of sub-units to the Western Front to assist with ammunition supply in the field, and the operation of supply dumps.

Re-amalgamation
As noted above the artillery arms were re-amalgamated into the Royal Artillery in 1924 and the RGA then ceased to exist as a separate entity.