The BL 18-inch Mk I naval gun was a breech-loading naval rifle used by the Royal Navy during World War I. It was the largest and heaviest gun ever used
higher projectile velocities. The Mk X increased the bore length from the Mk IX's 480 to 540 in (12 to 14 metres), increasing muzzlevelocity from 2,600 to
The BL 15-inch Mark I succeeded the BL 13.5-inch Mk V naval gun. It was the first British 15-inch (380 mm) gun design and the most widely used and longest
earlier 15-inch Mk I gun, which fired a heavy shell at a rather low muzzlevelocity, and instead fired a rather light shell at a high muzzlevelocity; this