The gun intended for the "Super Fast Battlecruiser" was the 17in/45

As I have previously mentioned, I had a design for a 17in/45 gun that fired an AP shot of 2,814 lbs. The muzzle velocity was 2,850 ft/sec. The muzzle energy was 158,397 foot-tons. The length was 63.75 ft. This was to form the main armament of the so-called "Super Fast Battlecruiser", which was to supercede the GB/CB/1905, GB/CB/1907, and GB/CB/1910 ships.