The N3's 16.5-inch gun

What calibre was intended for the N3 battleships, and what would its firing cycle look like?

Admiralty specifications, British calibre progression, and shell data support a 16.5-inch/45 weapon with a rate near two rounds per minute; larger calibres would begin to slow the cycle.

The N3 specification called for 16.5-inch rather than 16-inch or 18-inch guns. Admiralty documents, the Royal Navy's pattern of increasing calibre in 1.5-inch steps, and the shell weights associated with the project support that reading. Surviving paper trails for experimental heavy guns are uneven, so test pieces are harder to trace than design specifications. A later follow-up keeps the expected firing rate near two rounds per minute at 16.5 inches, while warning that 17-inch weapons would begin stretching the reload cycle beyond thirty seconds.