Related Rule
Practice Relating to Rule 8. Definition of Military Objectives
Section G. Economic installations
Belgium’s Law of War Manual (1983) states:
The purpose of combat between belligerents is to weaken and eliminate the power of resistance of the enemy.
This resistance is provided in the first place by the armed forces of a Party to the conflict. As a result, acts of violence are in the first place directed against the military potential of the adversary (the army, its positions, provision of its supplies, its stores, workshops, arsenals, depots, defence works, vehicles, aircraft, war buildings, etc.).
But this resistance also depends on the economic power of the adversary (its war industry, its production capacity, its sources of supply, etc.); in short, its economic potential. The breaking up of this economic potential has of course a direct influence on the armed forces’ capacity to resist, so that this economic potential also becomes a war objective. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 26.