This difference in structural integrity also determined the number of cannons that could be carried on board. Because the Japanese ships lacked the strength to withstand the recoil of cannon, even the largest ship class, Atakebune, could carry only four at most (six if there were two smaller breech loading swivel guns). A Sekibune could only carry two. A panokseon could carry at least 20 cannons, but usually carried more (maybe up to 50). Since the hulls of Korean warships were strong enough, moreover, they were able to carry a large number of long-range cannons. These could be installed with ease on the large upper-deck of panokseon ships, and their angle configured at will to increase the range. Since the Japanese warships only allowed for a very limited number of cannons, their sailors mainly used muskets, which had a range of 100–200 m (330–660 ft) and Japanese naval commanders were sure that a volley of musket bullets would clear the enemy ships and allow for the grapple and board method.