St. Mary—a small, wooden-hulled, side-wheel steamer built at Plaquemine, Louisiana—was presented to the Confederate government upon completion early in 1862.

Protected by bales of cotton, the vessel operated on the Yazoo and Tallahatchie Rivers for the remainder of that year and into the summer of 1863.

On 13 July, a Union joint Army-Navy expedition of four warships and 5,000 troops captured St. Mary at Yazoo City, Mississippi.

On 18 September 1863, Rear Admiral David Dixon Porter wrote to the Secretary of the Navy, Gideon Welles, requesting permission to retain the prize for naval service and asking that the ship be renamed Yazoo.

Although surviving records are not conclusive, it seems that after the prize had been repaired, Admiral Porter may have used the steamer in the autumn as a non-commissioned dispatch boat.