The turtle ships designed by Yi held eleven cannons on each side of the ship, with two each at the stern and the bow. The ship's figurehead was in the shape of a dragon. The figurehead itself held up to four cannons, and emitted a smokescreen that, in combination with its fierce appearance, was meant to be used as psychological warfare. The sides of the turtle ship were dotted with smaller holes from which arrows, guns, and mortars could be fired. The roof was covered with planks and spikes. The purpose of the spikes was to prevent the ship from being boarded by the enemy. The larger Japanese ships' sides were higher than the turtle ships' and thus, the spikes prevented boarders from jumping down onto the roof without risking impalement. There were two masts that held two large sails. The turtle ship was also steered and powered by twenty oars, each of which were pulled by two men during fair conditions and five in foul seas or combat.