During the late 18th century, the first coastal defenses built in the United States were earthen forts constructed on high points near important harbors. Soon thereafter, star-shaped stone forts were built in the years leading up to the War of 1812. Fort McHenry in Baltimore and Fort Wood (now Liberty Island) in New York Harbor were examples of this type of fortification. After the War of 1812, hexagonal forts like Fort Sumter in Charleston, South Carolina were built. From 1890 to 1910, concrete batteries with big guns began to replace concentrated forts. Fort Mott in Pennsville, New Jersey is an example of this kind of dispersed fortification. In 1905, Secretary of War Taft, under President Theodore Roosevelt, added searchlights and electrification to these forts. The Taft system also added mathematical triangulation to aim the guns at enemy shipping.
This system was still in use during World War II.
With each generation of coastal defense, fewer fortifications were required. And as guns became more and more powerful, forts could be moved further and further away from the harbors that they protected. With the construction of Fort Miles in 1940, the Harbor Defenses of the Delaware had moved fully 100 miles South of the Port of Philadelphia.
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