Measuring air defence by the attack it prevents

Should air defence be judged by preventing the enemy's mission rather than by aircraft kills?

Yes. Preventing aircraft from completing their attack is the central task, and that priority helps distinguish naval from land-based fighter doctrine in the Second World War.

Air defence succeeds when enemy aircraft cannot complete their mission, even if the attackers survive. Aircraft kills alone therefore provide an incomplete measure of its effectiveness. This priority helps explain differences between naval and land-based fighter doctrine in the Second World War.