Glasgow and the Clyde estuary was designated as Class B harbour by the Home Ports Defence Committee, later the Home Defence Committee with defences designed to resist attack from armoured cruisers.
By the end of the 19th Century the Clyde Estuary had coastal defences at:
- Ardhallow Battery constructed between 1901 and 1905 with two 6-inch Mark VII guns.
- Portkill Battery built between 1900 and 1904 with two 6-inch Mark VII guns and two 4.7-inch Q.F. guns
- Fort Matlida originally built in 1858 but redeveloped between 1895 and 1905 to mount two 4.7-inch Q.F. guns.