The defense of the Hudson River against British ships was an important task of the Revolutionary Army. The river's sharp bend and strong currents at this point made Constitution Island well located for this purpose.
Construction on Fort Constitution began in late 1775 but was halted three months later upon realization of the fort's many shortcomings. Work on the island fortifications was transferred to Marine, Hill Cliff, and Gravel Hill Batteries, better sited for firing down river. The major defense of the Hudson was shifted five miles south to Forts Montgomery and Clinton, where a chain was placed across the river. Those forts and the Constitution Island fortifications were destroyed in October 1777 during British operations on the Hudson. This British force, advancing up river to aid Burgoyne's army invading from Canada, returned to its New York City base after learning of Burgoyne's surrender at Saratoga.
In 1778, taking advantage of commanding high ground, determined patriots built new Hudson fortifications at West Point. From there a great chain and boom stretched across the river to Constitution Island, where two river batteries and three redoubts were constructed. This West Point garrison, including Constitution Island, was never attacked.
The number of soldiers on Constitution Island varied from approximately 130 men at the time the island was abandoned to the British in 1777 to several regiments posted to work details when the island was part of the West Point garrison. During those latter years, approximately 400 men - - one seventh of the total West Point strength - - were deemed necessary to defend Constitution Island from attack. In creating fields of fire, obtaining construction material, and providing fire wood, the soldiers stripped the island treeless. A slaughter house, a storehouse, smithy, three barracks, huts, tenting sites, and perhaps other essential facilities supported the garrison during some part of the island's Revolutionary War History.