 Faced with the limitations of the technology of the day, Pook decided that the hull should be built with three keels, the outboard pair somewhat longer than the one on the centerline.Propulsion would be provided by a single paddlewheel, immediately aft of the center keel; perhaps unintentionally, this meant that it would be somewhat protected from enemy projectiles by the armor carried along the sides.The contract for constructing the seven gunboats was awarded to Eads and was signed on 7 August 1861.