Coastal defence and fortification

With the rise of the submarine threat at the beginning of the 20th century, anti-submarine nets were used extensively, usually added to boom defences, with major warships often being equipped with them (to allow rapid deployment once the ship was anchored or moored) through early World War I.

For example, in the late Roman period the Saxon Shore was a system of forts at the mouths of navigable rivers, and watch towers along the coast of Britannia and Gaul.

In addition there was a system of fortified towns, burghs, that were positioned at choke points along navigable rivers to prevent raiders from sailing inland.

Fort Louvois is on a built-up island, 400 meters (1,312 ft) from the shore, and connected to it by a causeway that high tide completely submerses.

In Colonial times the Spanish Empire diverted significant resources to fortify the Chilean coast as consequence of Dutch and English raids.

[5] The Dutch occupation of Valdivia in 1643 caused great alarm among Spanish authorities and triggered the construction of the Valdivian Fort System that begun in 1645.

Other vulnerable localities of colonial Chile such as Chiloé Archipelago, Concepción, Juan Fernández Islands and Valparaíso were also made ready for an eventual English attack.

[8][5] Inspired in the recommendations of former governor Santa María the Spanish founded the "city-fort" of Ancud in 1768 and separated Chiloé from the Captaincy General of Chile into a direct dependency of the Viceroyalty of Peru.

[9] China first established formal coastal defences during the early Ming dynasty (14th century) to protect against attacks by pirates (wokou).

[12] Taiwan has several coastal fortifications, with some, such as Fort Zeelandia or Anping Castle dating to the time of the Dutch East India Company.

Prior to the American Revolution many coastal fortifications already dotted the Atlantic coast, as protection from pirate raids and foreign incursions.

The Revolutionary War led to the construction of many additional fortifications, mostly comprising simple earthworks erected to meet specific threats.

[16] 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.

[16][17] 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.

Under a major program developed in the wake of the Fall of France in 1940, a near-total replacement of previous coast defenses was implemented, centered on 16-inch guns in new casemated batteries.

On 13 June 1942 Seaman 2nd Class John Cullen, patrolling the beach in Amagansett, New York, discovered the first landing of German saboteurs in Operation Pastorius.

Cullen was the first American who actually came in contact with the enemy on the shores of the United States during the war and his report led to the capture of the German sabotage team.

In the early Victorian era, Alderney was strongly fortified to provide a massive anchorage for the British Navy before France became an ally of Britain in the Crimean War, even so plans changed slowly and the Palmerston Forts, a group of forts and associated structures were 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.

[19] 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'"[20] 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.

The Maunsell Forts were small fortified towers, primarily for anti-aircraft guns, built in the Thames and Mersey estuaries during the Second World War.