On 19 May 1846, only six days after President James Polk signed the Declaration of War with Mexico, Secretary of the Navy George Bancroft authorized the purchase of Spitfire and Vixen, two light draft steamers being built for the Mexican Navy. The ships were delivered to the United States Navy on 14 July 1846, and Spitfire was commissioned on 21 August 1846, Commander Josiah Tattnall in command.