 Swiftsure's secondary armament consisted of fourteen 50-calibre 7.5-inch Mk III guns. Ten of the guns were mounted in a central battery on the main deck; the other four were in casemates abreast the fore- and mainmasts on the upper deck. A major problem with the guns on the main deck was that they were mounted low in the ship — only about 10 feet (3 m) above water at deep load — and were unusable at high speed or in heavy weather as they dipped their muzzles in the sea when rolling more than 14 °. The guns fired 200-pound (91 kg) projectiles at a muzzle velocity of 2,781 ft / s (848 m / s) at a rate of four rounds per minutes. At their maximum elevation of 15°they had a maximum range of about 14,000 yards (13,000 m). The ship carried 150 rounds per gun.
