The Hudson River was blocked to British ships during the Revolutionary war by a sixty-five-ton iron chain. David Levine tells this TALE in the HEAR and THEN and in his book, The Hudson Valley: The First 250 Million Years”( Bookshop.org and Amazon ).
The Hudson was seen as a key to victory during the American Revolution. The British controlled New York City and Canada with the Hudson, Lake George and Lake Champlain water corridor lying between them. The patriots needed a way to stop British boats from traveling upstream. Captain Thomas Machin, an English-born patriot, suggested using a large iron chain floated across the river and anchored to both shores.
Such a chain was tried at Fort Montgomery in 1777, but did not stop the British as they attacked the troops on shore instead. A chain was floated at West Point but this time Tadeusz Kościuszko fortified West Point to protect the chain at the shore. The chain held and prevented incursions up the River and raids that occurred elsewhere. The need for the British to circumvent the chain was so pressing that that it ended up in a treasonous chapter by a certain patriot General.