USS Ammonoosuc, a 3850-ton steam frigate, was built at the Boston Navy Yard, Massachusetts, as part of a Civil War program of large, very fast, steam cruisers. Launched in July 1864, her completion was delayed when the war ended. After installation of her engines at New York, she ran trials in June 1868, attaining the then-extraordinary speed of over 17 knots. After trials, Ammonoosuc was laid up at Boston. Renamed Iowa in May 1869, she saw no active service and was finally sold in September 1883.