Why the first British super-dreadnoughts used 13.5-inch guns

Why did Britain choose the 13.5-inch gun instead of a 14-inch gun for its first super-dreadnoughts?

Manufacturer competition was decisive: the more attractive available gun came from Armstrong, while Vickers was pushing the 14-inch alternative.

An Elswick 14-inch offering might have led Britain to choose that calibre. The available 14-inch proposal was associated with Vickers, while Armstrong offered the stronger 13.5-inch weapon. Practical weapon quality and the standing of the manufacturer able to supply it shaped the decision. The resulting calibre choice was as much an industrial procurement outcome as a ballistic one.