Gunports for early gunpowder artillery had begun to be installed in English castles during the 15th century. At Kirby Muxloe, six gunports were constructed in the ground floor walls of both the gatehouse and west tower; these were then temporarily filled with bricks, probably to prevent vermin and to limit the draughts. Several more gunports were built lower down in the gatehouse, presumably in error as they were ultimately below the waterline of the moat and permanently blocked up. The range of any guns at the castle would have been quite limited, as they were positioned relatively low to the ground. Historians are uncertain to what extent any guns at Kirby Muxloe would have been useful in a conflict. The gunports are of early design and may have been intended to be symbolic rather than practical; they were well positioned across the castle's defences, however, and might well have been intended to deter a serious attack.