Portland was designated as a Class B harbour by the Home Ports Defence Committee, later the Home Defence Committee and was intended to resist attack from armoured cruisers.
Over the years a number of coastal defenses were built but by 1914 there were four main sites:
- Breakwater Fort was a single tier armoured fort with 14 guns in casemates that was built between 1861 and 1875. Between 1908 and 1909 two 6-inch Mark VII were mounted on the roof of the old casemates.
- Inner Pier Head Fort for which was a circular fort constructed on the south breakwater between 1859 and 1862 by the Admiralty. It was then taken over by the War Department and between 1897 and 1899 armed with two 12-pdr Q.F. gun mounted on the roof of the original fort.
- A Pier Head
- B Pier Head
- C Pier Head
- East Weare Battery which included a number of earthen positions which mounted Rifle Muzzle Loading guns. These were designated as Battery A through to E, some five locations. Between 1899 and 1901 the ‘A’ and ‘B’ Batteries (most southernly) were upgraded to mount two 9.2-inch Marks X guns and three 6-inch Mark VII guns respectively.
- Blacknor Battery which was built between 1900 and 1902 and then rearmed between 1905 and 1906. Armed with two 9.2-inch guns.
- Nothe Fort was a granite fort built between 1860 and 1872 with ten Rifle Muzzle Loading guns in casemates. Between 1902 and 1904 three 6-inch Mark VII guns were mounted on the roof.
- Verne Citadel on the escarpment above Queens Town.
- Upton Battery