During the war, he first served aboard . Promoted to lieutenant on July 16, 1862, he served briefly in the steam sloop before transferring to the squadron on the Mississippi River late in 1862. On November 8, 1862, he received orders to assume command of the stern-wheel casemate gunboat . Bache commanded the gunboat during operations leading up to the fall of Vicksburg, Mississippi, early in July 1863. During those operations, however, his ship was sunk on May 27, 1863, while dueling Confederate batteries defending the river approaches to the city.