Based on in-game data compiled by Hammer and the WW2 Weapon Lethality calculations of Tony Williams.
Hammer's RtKH data is based on the rounds to kill a hangar in-game; Hammer's calculated figures are derived from a 1-second fired burst for TW data. (Normalized to 1 M2 .50cal = 10)
Based on in-game data compiled by Hammer. 'Primary' is the 'main gun' - usually cannons; 'secondary' is usually machine guns or the smaller battery.