Clarke relates the 6.5-inch gun to an older 42-pounder cannon category, drawing on conversations with specialists in French arms. On that explanation, the Dupleix battery follows a mixed 42-pounder and 9-pounder arrangement expressed in newer calibre measurements. Older cannon conventions help account for some apparently unusual French metric calibres. Mogador's gun diameter is offered as a further example, equated to an 18-pounder.
Notable Point · 3:22:15-3:23:42
French gun calibres and older pounder conventions
Unusual-looking French gun calibres are related to older pounder categories in an explanation of the Dupleix class's mixed battery.