The screw sloop _Hartford_, launched at Charlestown in 1858, was one of a follow-up class of steamers. (These and other screw steamers of the ’50s were all frigates and sloops; no steam ship-of-the-line was built at Charlestown or any other yard. As we have seen, the era of such large wooden ships was over by the time the Navy was converting to steam.) These were smaller vessels with a shallower draft—better suited to coastal and river operations. As Rear Admiral David G. Farragut’s flagship in victories at New Orleans and Mobile Bay, _Hartford_ was perhaps the most celebrated steamer in the Union Navy. With propellers, even the most hidebound captains could appreciate the better maneuverability steam gave them during combat. Gradually the tactical roles of steam and sail were reversed, with increasingly efficient and dependable steam engines officially becoming the primary power source and sail the auxiliary. As a matter of economy, however, American vessels continued to use sail whenever possible on long-distance cruises. Steam technology demanded a whole new set of skills of Charlestown’s mechanics. When the steam battery _Fulton II_ docked there in 1839, the yard could repair only the vessel’s wooden components, having to contract work on the engine to local companies. But by 1845 yard personnel could fully service the screw sloop _Princeton_. While some carpenters may have made the transition, it is more likely that most of those working with steam machinery had a background in the field. As the yard adapted to the new age, it underwent a decade of modernization and quickened production preceding the Civil War. The dry dock was lengthened; gas lights were installed; the yard began manufacturing wire rope in 1857. But the most important improvement was a state-of-the-art machine shop—its 240-foot stack long a landmark at the yard—that replaced the old smithery in 1859. It contained such equipment as a machine that could plane a metal surface 10 feet square and a huge lathe capable of handling iron propeller shafts 35 feet long. The facility also helped the yard to incorporate a new technology dramatized (though not introduced) by C.S.S. _Virginia_: ironcladding.