early in 1864, the commander of the army of the cumberland, major general george h. thomas, was seeking a light-weight, easy-to-haul and erect pontoon bridge to move his troops across unfordable rivers and streams. knowing the limitations of the two systems used by the armies in the western theater, he had folding pontoons developed. a similar idea had been instigated by his predecessor william s. rosecrans earlier in the war, but had not been adopted. captain william e. merrill, thomas's chief engineer, improved on rosecrans's prototype, making it lighter and stronger. he replaced the pins that held individual sections together with hinges so that the side frame sections folded together instead of separating. the new design yielded a portable boat that was lightweight, small enough to carry on a standard supply wagon, and easier to construct in the field. it was also strong enough to support horse-drawn artillery and fully loaded wagons.