Three ships of the United States Navy have borne the name USS Merrimack, named in honor of the Merrimack 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, two other US Navy ships have borne the name Merrimac, a variant spelling of Merrimack.

• The first Merrimack , was a ship launched by an Association of Newburyport Shipwrights and presented to the Navy in 1798. She was stripped of naval equipment and sold in 1801. Subsequently, while operating in merchant service under the name Monticello, the ship was lost off Cape Cod, Mass.

• The second Merrimack, was a screw frigate, commissioned in 1856 and decommissioned in 1860. In 1861 she was burnt in an attempt to avoid capture during the American Civil War, but her hull and engines were used as the basis for the first CSS Virginia

• The third Merrimack , (AO-37), a fleet oiler, was acquired by the Navy in 1941; renamed and commissioned in 1942. She served in both the Atlantic and Pacific during World War II, and was finally struck from the Navy list in 1959.