"Majestic" and her sisters were armed with four BL 12-inch Mk VIII 35-calibre guns in twin-gun turrets, one forward and one aft. This calibre would become the standard for all British battleship classes built for the next fifteen years. They were the first new British battleships to mount a 12-inch main battery since the 1880s. The new gun was a significant improvement on the 13.5-inch (343 mm) gun which had been fitted on the Admiral and "Royal Sovereign" classes that preceded the "Majestic"s, in terms of ballistics and strength of the gun itself, and it was significantly lighter. The 12 in gun had a muzzle velocity of —a significant increase over the 13.5 in gun owing to the use of smokeless propellant—and it could fire a shell with a range of .