Chevaux-de-Frise Deployed in the Hudson

To supplement the forts' cannon fire, the Americans sank chevaux-de-frise — heavy wooden frames studded with iron-tipped spikes — in the Hudson River between Fort Washington and Fort Lee. These underwater obstacles were designed to damage or sink British ships attempting to pass upriver.

The chevaux-de-frise proved ineffective. British vessels navigated around or through them with limited damage. The failure of the river obstructions, combined with the inability of the forts' guns to stop ships in a wide river, meant that the entire defensive concept was flawed. The costly investment in the twin-fort strategy consumed resources and manpower that might have been used more effectively elsewhere.