For this comparison, an ideal destroyer acts as both shield and spear for the fleet. It needs weapons to attack targets as well as defend against incoming threats. A design dominated by attack approaches an enlarged torpedo boat, while a gun-only defensive ship approaches a flak frigate. The Type 31 is offered as a legitimate example of the latter role, but the destroyer standard requires a balance between the two missions.
Chapter · 8:40-10:11
The shield-and-spear test for destroyers
The ideal-destroyer criterion requires enough offensive and defensive capability to attack enemies while protecting a formation.