Coastal defence and fortification
Coastal defence (Commonwealth and Ireland) or coastal defense (US) and coastal fortification are measures taken to provide protection against attack by military and naval forces at or near the shoreline. Because an invading enemy normally required a port or harbour to sustain operations, such defences are usually concentrated around such facilities, or places where such facilities could be constructed.
Sea forts 
Although most coastal fortifications are on the coast, not all are. Instead, some are off the coast on islands, artificial islands, or are specially built structures. All the sea forts share the characteristic that at least at high tide they are completely surrounded by water. Some, such as Fort Denison or Fort Sumter, are actually in harbours, but most are off the coast. Again, some, such as for example Bréhon Tower, completely occupy small islands, although others, such as for example Flakfortet and Pampus, are on artificial islands built up on shoals. Fort Louvois is on a built-up island, 400 meters from the shore, and connected to it by a causeway that high tide completely submerses. The most elaborate sea fort is Murud-Janjira, which is so extensive that one might truly call it a sea fortress.
The most recent sea forts were the Maunsell Forts, which the British built during World War II. One type consisted of a concrete pontoon barge on which stood two cylindrical towers on top of which was the gun platform mounting. They were laid down in dry dock and assembled as complete units. They were then fitted out before being towed out and sunk onto their sand bank positions in 1942. The other type consisted of seven interconnected steel platforms built on stilts. Five platforms carried guns arranged in a semicircle around the sixth platform, which contained the control centre and accommodation. The seventh platform, set further out than the gun towers, was the searchlight tower.
Coastal defence and fortification by country 
China first established formal coastal defences during the early Ming dynasty (14th century) to protect against attacks by pirates (wokou). Coastal defences were maintained through both the Ming dynasty and the Qing dynasty that followed, protecting the coast against pirates, and against the Portuguese and other European powers that sought to impose their will on China.
Subsequently, the European powers built their own coastal defences to protect the various colonial enclaves that they established along the Chinese coast. One such, a fort built by the British commanding the Lei Yue Mun channel between Hong Kong Island and the mainland, has been converted into the Hong Kong Museum of Coastal Defence. This tells the story of coastal defence along the South China coast from the Ming dynasty onwards.
New Zealand 
The coastline of New Zealand was fortified in two main waves. The first wave occurred around 1885 and was a response to fears of an attack by Russia. The second wave occurred during World War II and was due to fears of invasion by the Japanese.
The fortifications were built from British designs adapted to New Zealand conditions. These installations typically included gun emplacements, pill boxes, fire command or observation posts, camouflage strategies, underground bunkers, sometimes with interconnected tunnels, containing magazines, supply and plotting rooms and protected engine rooms supplying power to the gun turrets and searchlights.
Taiwan has several coastal fortifications, with some, such as Fort Zeelandia or Anping Castle dating to the time of the Dutch East India Company. Others, such as Cihou Fort, Eternal Golden Castle, Hobe Fort, date more to the end of the 19th Century. The Uhrshawan Battery dates primarily to the first-half of the 19th Century. It actually underwent bombardment during the Sino-French War.
United States 
The defence of its coasts was a major concern for the United States from its independence. Prior to the American Revolution many coastal fortifications already dotted the Atlantic coast, as protection from pirate raids and foreign incursions. The Revolution led to the construction of many additional fortifications, mostly comprising simple earthworks erected to meet specific threats.
The prospect of war with European powers in the 1790s led to a national programme of fortification building spanning seventy years in three phases, known as the First, Second and Third Systems. By the time of the American Civil War, advances in armour and weapons had made masonry forts obsolete, and the combatants discovered that their steamships and ironclad warships could penetrate Third System defences with acceptable losses.
In 1885 US President Grover Cleveland appointed the Endicott Board, whose recommendations would lead to a large-scale modernization programme of harbour and coastal defences in the United States, especially the construction of well dispersed, open topped reinforced concrete emplacements protected by sloped earthworks. Many of these featured disappearing guns, which sat protected behind the walls, but could be raised to fire. Mine fields were a critical component of the defence, and smaller guns were also employed to protect the mine fields from minesweeping vessels.
The development of military aviation rendered these open topped emplacements vulnerable to air attack. Therefore, the next, and last, generation of coastal artillery was mounted under thick concrete shields covered with vegetation to make them virtually invisible from above. In anticipation of a conflict with Japan, most of the limited funds available between 1933 and 1938 were spent on the Pacific coast. In 1939 the threat of war in Europe prompted larger appropriations and the resumption of work along the Atlantic coast.
United Kingdom 
The walls around coastal cities, such as Southampton had evolved from simpler Norman fortifications by the start of the 13th century. Later, King Edward I was a prolific castle builder and sites such as Conwy Castle, built 1283 to 1289, defend river approaches as well as the surrounding land. Built 1539 to 1544, the Device Forts are a series of artillery fortifications built for Henry VIII to defend the southern coast of England. Between 1804 and 1812 the British authorities built a chain of towers known as Martello Towers to defend the south and east coast of England, Ireland, Jersey and Guernsey against possible invasion from France. The Palmerston Forts are a group of forts and associated structures built during the Victorian period on the recommendations of the 1860 Royal Commission on the Defence of the United Kingdom, following concerns about the strength of the French Navy. In 1865 Lieutenant Arthur Campbell Walker, of the School of Musketry advocated the use of armoured trains on "an iron high-road running parallel with that other 'silent highway', the source of all our greatness, the ocean, our time-honoured 'moat and circumvallation'" During the First World War the British Admiralty designed eight towers code named M-N that were to be built and positioned in the Straits of Dover to protect allied merchant shipping from German U-boats. Nab Tower is still in situ. The Maunsell Forts were small fortified towers built in the Thames and Mersey estuaries during the Second World War
See also 
- "Coastal Defense". GlobalSecurity.org. Retrieved 2009-11-29.
- "Gallery 2: The Ming Period (1368-1644)". Hong Kong Museum of Coastal Defence. Retrieved 2009-11-29.
- Baigent, Captain AJ (1959). "Coast Artillery Defences". Royal New Zealand Artillery Association. Retrieved 2009-11-29.
- "Coastal Defense". United States National Parks Service. Retrieved 2009-11-29.
- Brown, D. (2006). "Palmerston and Anglo--French Relations, 1846--1865". Diplomacy & Statecraft 17 (4): 675–692. doi:10.1080/09592290600942918.
- Walker, Arthur (2000 (Original work published 1865)). "Coast Railways and Railway Artillery". Journal of the Royal United Services Institute. Pallas Armata. pp. 221 – 234.