Placing the propellant magazine below the shell room allows a low mine or torpedo hit to admit water where a fire would be especially dangerous. British arrangements changed after the 15-inch Mark I to put those spaces in this order. Flooding remains a serious threat, but a fire in a confined magazine can create a much more destructive outcome. An explosion also does not always sink the whole ship: ships sometimes lost a bow or stern and remained afloat. The extent of flooding after the damaged section is lost matters to whether the remaining hull survives.
Notable Point · 4:45:35-4:47:49
Why flooding could be preferable to a magazine fire
Magazine position can favor flooding over fire after an underwater hit, while loss of a bow or stern need not sink the remaining hull.