A new round of fortification building began in the United States and its overseas territories in the late-19th century, which benefited from the latest technology and the increase in America's worldwide economic stature. This book provides a concise introduction to the design, development and purpose of American coastal defenses in the 'modern period' (1885-1950), a period defined by the use of concrete, steel, and powerful breech-loading rifles. Packed with period and modern-day images of the fortifications, and written by a leading expert, it covers the emplacements, weaponry, equipment, and people that defended their country in times of great change and uncertainty.