In the spring of 1778, the most notable of all these obstructions, a heavy chain supported by huge logs, was stretched across the Hudson from West Point to Constitution Island. It was constructed at the Sterling Iron Works, in Warwick Orange County, by Peter Townsend, under the supervision of Timothy Pickering. The task was completed in six weeks. Chevaux-de-frise were also placed in the channel between Pollopel's Island and the western shore of the river, just above the North Gate of the Hudson Highlands.
The links were carted to New Windsor, where, at Captain Machin's forges, they were put together, and the whole floated down the river to West Point on logs late in April. The links weighed from 100 to 150 lb (46 to 68 kg) each. The length of the chain was 1,500 feet (457 m), and its entire weight was 186 tons. The logs that buoyed it were placed transversely with the chain, a few feet apart, and their ends secured by chains and strong timbers. The ends were made secure to the rocks on both shores on April 30, 1778. Fort Constitution, on Constitution Island, defended one end, and a small battery the other. In winter it was drawn on shore by a windlass, and replaced in the spring. The British never attempted to disturb it; but it was said that Benedict Arnold, when he prepared for the execution of his treason, took measures for weakening the chain — how is not stated. Peter Townsend received a great sum of money from the Continental Congress for performing the work.
The chain was a part of fortifications designed and built by Tadeusz Kosciuszko.From Wikipedia