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Coastal defence (or defense) and coastal fortification are measures taken to provide protection against military attack at or near a coastline (or other shoreline), for example, fortification and coastal artillery. Because an invading enemy normally requires a port or harbour to sustain operations, such defences are usually concentrated around such facilities, or places where such facilities could be constructed.〔(【引用サイトリンク】title=Coastal Defense )〕 In littoral warfare, coastal defence counteracts naval offence, such as naval artillery, naval infantry (marines), or both. ==Sea forts== Sea forts are completely surrounded by water - if not permanently, then at least at high tide. Unlike most coastal fortifications, which are on the coast, sea forts are not. Instead, they are off the coast on islands, artificial islands, or are specially built structures. Some sea forts, such as Fort Denison or Fort Sumter, are within harbours in proximity to the coast, but most are at some distance 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Coastal defence and fortification」の詳細全文を読む スポンサード リンク
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