Greater speed in production of submarine chasers has been achieved by adding a “bottoms up” technique to assembly line methods at the yards of Dravo Corporation of Pittsburgh, Pa. The 173- foot craft are built in an upside-down position, which facilitates the welding of the hull sections. Specially rigged gantry cranes turn the hull sections right-side up, and powerful hydraulic jack-operated transfer carriages are used to move them along to the final assembly line.