Two ships of the United States Navy have borne the name USS Merrimac, named in honor of the Merrimack River (also known as the Merrimac River), a river formed by the junction of Pemigewasset and Winnipesaukee Rivers at Franklin, New Hampshire. The Merrimack flows south across New Hampshire, and then eastward across northeastern Massachusetts before emptying in the Atlantic at Newburyport, Massachusetts.

Also, three other US Navy ships have borne the name Merrimack, including the frigate USS Merrimack (1855), which was converted into CSS Virginia, one of the first ironclad warships.

• The first Merrimac , was a sidewheel steamer purchased in England for the Confederate government in 1862 for use as a blockade runner. She was captured by USS Iroquois in 1863, and purchased by the Navy in 1864. Merrimac served from May to February 1865, when she foundered during a storm.

• The second Merrimac , was built as Solveig in 1894, and purchased by the Navy in April 1898. She was sunk off Santiago, Cuba in May, during the Spanish-American War.