Decatur sailed from Hampton Roads, Virginia 1 March 1847, and after a brief stay at the Pensacola Navy Yard, arrived off Castle Juan de Uloa, Mexico, 14 April, for duty in the Mexican-American War.
Although she was too large to ascend the Tuxpan River, 14 of her officers and 118 men accompanied Commodore Matthew C. Perry's expedition to attack Tuxpan.