The correct answer to fill up the blank is Merrimack.
In April 1854, the United States Congress authorized the construction of six similar warships, all named with river names. Created in 1855 and set up in Boston in December of the same year, the Merrimack was built in oak, it had the lines of a sailboat and was maneuvered easily even when it received only the thrust of the sails. The main weapon system was composed of Dahlgren cannons, a total of 40 fire hydrants. By the end of 1860, after five years of service, the Merrimack was towed into the naval arsenal of Norfolk, Virginia, due to some problems, and was still there when, on April 17, 1861, the state of Virginia separated from the Union. Three days later, the Union Navy abandoned the arsenal, burning, among others, seven important warships. Merrimack was one of them.