Useful for protection against Submarine attack, where aerial observation is a lesser factor.
Useful where greatest danger is from the air and high surface visibility must be accepted.
Measure 21 - Navy Blue System
Useful for combatant ships operating in areas where greatest danger might be expected from gunnery action either from shore batteries or from enemy surface ships. Moderately high visibility to aerial observation at close ranges.
Measure 22 - Graded System