The coast defences of the United Kingdom were defined to included defended ports, naval war signal stations, and cable landing places. The defended ports could be likened to military districts. Their headquarters and units were administered by the respective local Territorial Force Associations. The coast defence “units” listed on this page were manned by troops of the RGA Companies and can be cross-referenced with details from Royal Garrison Artillery Companies. Newly recruited men of the RGA would usualy train with such a Company after a brief preliminary period at an RGA Depot; they would usually then go on to be posted to a Heavy or Siege Battery.
In January 1914 newspapers reported much discussion about whether the Royal Navy should take over responsibility for coastal defence work and what would happen to the RGA if it did, but this was overtaken by events and it remained the responsibility of the RGA throughout the Great War.
Scottish Coast Defences
Known as Scotland Coast Defences until July 1908
- Clyde
- Headquarters and No. 1 Company: 7 King Street, Port Glasgow and included the defences of Fort Matilda
- No. 2 Company: Helensburgh with a station at Dumbarton
- No. 3 Company: Dumbarton
- Forth
- Heaquarters and Nos. 1 to 4 Companies: Easter Road Barracks in Edinburgh
- No. 5 Company: Kirkcaldy with a station at Kinghorn
- No. 6 Company: Burntisland with a station at Inverkeithing
- Orkney
- Heaquarters and Nos. 1 and 7 Companies: Kirkwall
- No. 2 Company: Sanday with a station at Stronsay
- No. 3 Company: Shapansay with a station at South Ronaldsway
- No. 4 Company: Stromness with a station at Finstown
- No. 5 Company: Evie with a station at Birsay
- No. 6 Company: Holm with stations at Deerness and Tankerness
- North Scottish
- Heaquarters and No. 3 Company: Broughty Ferry
- No. 1 Company: Fonthill Road, Aberdeen
- No. 2 Company: Cromarty with stations at Davidston, Jemimaville and Newhall
- No. 4 Company: Montrose
North Eastern Coast Defences
Known as Newcastle-on-Tyne Coast Defences until July 1908
- Durham
- Headquarters and No. 5 Company: The Armoury, West Hartlepool
- No. 1 Heavy Battery: Sunderland
- Nos. 2 to 4 Companies: West Hartlepool
- East Riding
- Headquarters and Nos. 1 to 4 Companies: Park Street, Hull
- Tynemouth
- Headquarters and Nos. 1 and 2 Conmpanies: Military Road, North Shields
- No. 3 Company: Seaton Delaval
- No. 4 Company: Blyth
North Western Coast Defences
Known as Mersey Coast Defences until July 1908
- Lancashire and Cheshire
- Headquarters and Nos. 1 to 4 Companies: 19 Low Hill, Liverpool
- Nos. 5 and 6 Companies: Riverview Road, Seacombe
- Nos. 7 and 8 Companies: Barrow-in-Furness
Eastern Coast Defences
Known as Thames and Medway and Harwich Coast Defences until July 1908
- Essex and Suffolk
- Headquarters: Main Road, Dovercourt
- No. 1 Company: Harwich with a station at Felixstowe
- No. 2 Company: Stratford
- No. 3 Company: Southend on Sea
- No. 4 Company: Ipswich
Western Coast Defences
Known as Wales Coast Defences until July 1908
- Glamorgan
- Headquarters and Nos. 1 to 3 Companies: Cardiff
- No. 4 Company: Penarth
- No. 5 Company: Barry
- Pembroke
- Headquarters and No. 1 Company: Milford Haven
- No. 2 Company: Saundersfoot with a station at Tenby
- No. 3 Company:Fishguard with a station at Pembroke Dock
Southern Coast Defences
Known as Portsmouth Coast Defences until July 1908
- Dorsetshire
- Headquarters: Lower St. Albands Street, Weymouth
- No. 1 Company: Swanage
- No. 2 Company: Poole with a station at Parkstone
- No. 3 Company: Portland with a station at Weymouth
- Hampshire
- Headquarters and Nos. 2, and 7 Companies: Southampton
- No. 1 Heavy Battery: Southampton with a station at Eastleigh
- No. 3 Company: Eastleigh with a station at Bishop’s Waltham
- No. 4 Company: Portsmouth
- No. 6 Company: Bitterne and Woolston
- No. 8 Company: Eastleigh

South Eastern Coast Defences
Known as Dover Coast Defences until July 1908
- Kent
- Headquarters: Sheerness
- No. 1 Company: Fort Clarence, Rochester with a station at Sheerness
- No. 2 Company: Gravesend with a station at Northfleet
- No. 3 Company: Dover with a station at Folkestone
- Sussex
- Headquarters and No. 1 Company: 17 Gloucester Road, Brighton
- No. 2 Company: Lewes
South Western Coast Defences
Known as Plymouth Coast Defences until July 1908
- Cornwall (Duke of Cornwall’s)
- Headquarters and No. 6 Company: Falmouth
- No. 1 Heavy Battery: Padstow with stations at Bugle, Charlestown, St. Merryn and Par
- No. 2 Heavy Battery: Penzance with stations at St. Buryan and St. Just
- No. 3 Company: Looe
- No. 4 Company: Marazion
- No. 5 Company: St. Ives
- No. 7 Company: Truro
- Devonshire
- Headquarters and Nos. 3 and 4 Companies: Lambay Hill, Plymouth
- No. 1 Heavy Battery: Ilfracombe with a station at Lynmouth
- No. 2 Heavy Battery: Devonport with stations at Plympton and Salcombe
- Nos. 5 and 6 Companies: Devonport

Note: Irish Coast Defences, which until July 1908 had been made up of Londonderry Coast Defences and Cork Coast Defences, was made up of the North Irish and South Irish Coast Defences. With Territorial Force having no base presence in Ireland, they were manned by the Antrim and Cork Royal Garrison Artillery (Special Reserve).
In 1918, the units manning the Defended Ports were reorganised into Fire Commands,