The rapid adoption of the 15-inch gun was an exceptional success at an earlier stage than Britain normally accepted a new weapon. An HMS Agincourt proposal, described in the discussion as an original Queen Elizabeth variant, is linked to 18-inch development through a circumstantial case: construction paused, small-tube boilers appeared as long-lead items, and the corresponding boiler order is otherwise missing. The later appearance of three 18-inch barrels for HMS Furious adds material evidence of a mature programme. Results from the 16.5-inch work and tests of German guns also fed the 16-inch programme associated with HMS Nelson and HMS Rodney. An 18-inch battleship project appears highly likely, although the surviving orders and design records do not provide the documentary smoking gun needed to prove the proposed ship and armament pairing. The supposed 20-inch programme leaves paperwork without comparable material evidence. The passage is also a lesson in historical method: strong inference still carries uncertainty.
Chapter · 20:07-23:00
British 16.5-inch and 18-inch work was more credible than a 20-inch leap
A plausible British progression through 16.5-inch and 18-inch programmes distinguishes material evidence and informed inference from proof of a ready 20-inch weapon.