The 8"/55 calibre gun (eight-inch-fifty-five-calibre) was the main armament weapon of US Navy heavy cruisers during World War II.
These were fitted in a variety of mounts with several different types of loading mechanisms during their 28-year career. The final (depicted in this training video) was a self-loading Mark 16 triple mount weighing about 20 tons, first fitted on the USS Des Moines.
Separate projectile and powder casings were loaded separately. The 35kg smokeless powder pack propelled a 152kg projectile at some 760 meters per second over a range of about 27km. The useful barrel life was about 780 rounds per gun.