The enthusiasm for the Volunteer movement following an invasion scare in 1859 saw the creation of many units composed of part-time soldiers eager to supplement the Regular British Army in time of need.

[15][16] The Glamorgan RGA was designated as a Defended Ports unit in Western Coast Defences, which was based at Pembroke Dock, and it had the following organisation:[5][13][17][18] The Glamorgan RGA mobilised in August 1914 as part of No 26 Coastal Fire Command, responsible for the following guns:[19][20] After the outbreak of war, TF units were invited to volunteer for Overseas Service and on 15 August 1914, the War Office (WO) issued instructions to separate those men who had signed up for Home Service only, and form these into reserve units.

[21] By October 1914, the campaign on the Western Front was bogging down into Trench warfare and there was an urgent need for batteries of siege artillery to be sent to France.

The WO decided that the TF coastal gunners were well enough trained to take over many of the duties in the coastal defences, releasing Regular RGA gunners for service in the field, and 1st line RGA companies that had volunteered for overseas service had been authorised to increase their strength by 50 per cent.

They also provided cadres to form new units for front line service, and the Glamorgan RGA is known to have raised at least five siege batteries in this way: 96th, 121st, 172nd, 359th and 402nd.

By this stage of the war, the Glamorgan RGA serving in the Swansea and Severn Defences of Western Command consisted of just three companies, the rest having formed batteries for overseas service.

These companies were given a slightly higher establishment (five officers and 100 other ranks) and renumbered, abolishing the 1st and 2nd Line distinction:[23][24] In April 1918 the Cardiff/Barry Garrison manned guns as follows:[25] The Swansea Garrison manned: According to WO Instruction No 181 of 16 December 1915, 96th Siege Battery was to be formed at Pembroke Dock by three officers and 78 other ranks (the establishment of a full company) drawn from the Glamorgan RGA.

[28] It went out to the Western Front on 21 May 1916 and joined 19th Heavy Artillery Group in Third Army on 25 May, taking over four 9.2-inch howitzers in existing emplacements near Pommier from 62nd Siege Bty.

[31][32] As the final bombardment began on Z Day (1 July), the battery fired with such intensity that the oil in the guns' hydraulic recoil buffers boiled.

By 1 November the Austrian army had collapsed and the pursuing British troops had left their heavy guns far in the rear.

[27] It trained as a BL 12-inch railway howitzer battery and went out to the Western Front on 10 June 1917, joining 19th HAG with XV Corps on the Flanders coast.

When the TF was reconstituted as the Territorial Army (TA) in 1921, the unit was designated as the Glamorgan Coast Brigade, RGA.

[9][60] Cardiff and Barry were designated Class A defended ports, with guns installed in peacetime, though the defence schemes of both were still being prepared.

Although this mainly involved the likely invasion areas of South and South-East England, an emergency battery of two BL 6-inch Mk XII naval guns was authorised on 12 June for Penarth, and two more of two BL 4-inch Mk VII naval guns each were authorised for Llanelli and Port Talbot on 21 July and completed by 24 August.

531st Rgt lost four of its batteries to two new coast regiments, 570th and 571st, formed from Flat Holm and Brean Down Fire Control respectively, while 192 Bty was disbanded.

By this stage of the war many of the coast battery positions were manned by Home Guard detachments or in the hands of care and maintenance parties.

[63][64][67][71][75][76] 570th Coast Rgt itself was disbanded at Barry on 1 June 1945, shortly after VE Day, together with 170, 184, 187, 189, 205, 366, 422, 430 and 431 Btys; the remaining TA batteries (145, 146 and 299) went into suspended animation.

[16][80][81][85][86][87][88] The following served as Honorary Colonel of the unit:[9] There is a stone tablet in St John the Baptist Church, Cardiff, as a memorial to the 69 men of the Glamorgan RGA who died during World War I.