The 15-inch/42 was one of several possible weapons: 13.5-inch and 16.5-inch alternatives appeared in the surrounding discussions, and Moore put his professional standing behind the selected gun. He could do so because it was far enough through development to be available on time, whereas the larger alternative was less mature. The ships also carried the latest fire-control equipment, reduced the main battery from ten guns to eight, and introduced higher speed. The episode counts the new gun, the eight-gun layout, and the extra speed as three major departures. That helps explain why the Admiralty resisted adding novel small-tube boilers as another major experiment.
Chapter · 22:04-25:30
The 15-inch gun and the three-change rule
The new 15-inch gun, an eight-gun layout, and higher speed already consumed the Royal Navy's usual tolerance for major changes between battleship classes.