Plymouth initially had defences concentrated around the dockyard area, including the Citadel and blockhouses.
Plymouth was subsequently designated as a Class A Port by the Home Ports Defence Committee, later the Home Defence Committee with a main Naval Base and Dockyard. Defences of the port were designed to resist attack by Battleships.
The first phase of new fortifications after the Napoleonic Wars were built between 1847 and 1849 and included:
- Picklecombe
- Staddon Point
- Eastern King (Prince of Wales Redoubt)
Picklecombe and Staddon Point were limestone casemated batteries mounting heavy guns. They were later redeveloped.
The 1860 Royal Commission recommended some 30 sites be developed and these were largely built between 1860 and 1872. The coastal defence fortifications outlined in the 1860 report were from west to east:
- Fort Scaresdon
- Fort Tregantle
- Plowhawn Battery
- Cawsand Fort
- Fort Picklecombe built between 1861 and 1868 with two levels of casemated gun batteries. The casemates held some 42 smoothbore guns
- Garden Battery constructed between 1862 and 1863 as a casemated battery for seven smoothbore gun
- Mount Wise Battery
- Western King’s Battery was built as an earthen works between 1862 and 1863
- Eastern King’s (Prince of Wales) was a masonry Redoubt from the 1840
- Drake’s Island Battery
- Two lower batteries, with twenty one guns in casemates built between 1860 and 1864
- Main Battery, on the highest point of the Island, which was constructed between 1868 and 1870
- Casemate Battery, again on the higher point of the Island, also constructed between 1868 and 1870
- Stamford Fort
- Staddon Heights Fort
- Brownhill Battery
- Twelve Acre Break Battery
- Watchouse Battery
- Bovisand Battery
- Breakwater Fort (sea fort)
The land defences for Plymouth from west to east were:
- Ernsettle Battery
- Agaton Fort
- Knowles Battery
- Woodland Fort
- Crown Hill Fort
- Bowden Fort
- Forder Battery
- Eggbuckland Keep (Defensible Barracks)
- Fort Austin
- Deerpark Emplacement
- Fort Efford
- Fort Laira
- Laira Battery
While the Royal Commission Forts of 1860 had been continually amended, the introduction of Rifled Muzzle Loading (RML) guns from 1870 onwards led to many changes. Between 1880 and 1900, when breech loading guns were fully introduced, the following additional fortifications were built:
- Tregantle Down Battery, just outside Tregantle Fort
- Whitesand Bay Battery, built between 1889 and 1894 with three 12.5-inch RML guns
- Rame Church Battery
- Penlee Battery
- Pier Cells (Brennan torpedo)
- Marker Battery
- Grenville Battery
- Hawkins Battery
- Raleigh Battery
- Picklecombe Battery (mentioned above)
- Mount Wise (mentioned above)
- Drakes Island, Upper (Main) Battery, Casemate Battery and Lower Battery.
- Staddon Height Battery
- Frobisher Battery
The final phase of development was the introduction of Breech Loading (BL) guns of 9.2-inch, 6-inch and 12-pdr calibre between 1900 and 1914. Some were mounted in old RML Batteries. These were:
- Whitsand Bay Battery (6-inch)
- Rame Church Battery, built between 1889 and 1895 with two high angle fire 9.2-inch Mark VI guns
- Penlee Battery built between 1890 and 1894 with three 9.2-inch Mark X guns
- Pier Cellers (12-pdr)
- Marker (6-inch)
- Hawkins (9.2-inch HA)
- Picklecombe Battery, built between 1908 and 1910 new positions on the roof for two 6-inch Mark VII gun and two 4-inch Q.F. guns
- Garden Battery, built between 1898 and 1900 it was rearmed with two 12-pdr Q.F. guns in two of the original casemates
- Western King’s seven 12-pdr Q.F. guns were mounted on these works in 1898 in two batteries
- Eastern King’s with four 12-pdr Q.F. guns being built on the original works in 1898
- Drakes Island with:
- Main Battery – Three 6-inch Breech Loading Guns
- Left Q.F. Battery – Three 12-pdr Quick Fire Guns
- Right Q.F. Battery – Three 12-pdr Quick Fire Guns
- Casemate Battery – Twenty one 9-inch RMLs in Casemated and shielded emplacements
- Main Battery – Three 11-inch and two 12.5-inch RML guns
- Three Defence Electric Lights
- Two Twin 6-pdr Quick Fire from World War
- Lord Howards Battery (6-inch)
- Watchouse Battery (6-inch)
- Fort Bovisand, four 12-pdr Q.F. guns were mounted on top of the battery between 1898 and 1899
- Lentney Battery(6-inch)
- Renney Battery (9.2-inch)
Plymouth Submarine Mining Establishment was built on a narrow strip of land between the Citadel and the harbour. Construction commenced in 1884 and the works were completed on 31st March 1888.