Protocol I to the Geneva Conventions, Article 52, provides for the general protection of civilian objects, hindering attacks to military objectives. Article 52 states, "In so far as objects are concerned, military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage."
Any attack must be justified by military necessity: An attack or action must be intended to help in the military defeat of the enemy, it must be an attack on a military objective, and the harm caused to civilians or civilian property must be proportional and not excessive in relation to the concrete and direct military advantage anticipated.
Legitimate military targets include: armed forces and persons who take part in the fighting; positions or installations occupied by armed forces as well as objectives that are directly contested in battle; military installations such as barracks, war ministries, munitions or fuel dumps, storage yards for vehicles, airfields, rocket launch ramps, and naval bases.
Legitimate infrastructure targets include lines and means of communication, command and control, railroad lines, roads, bridges, tunnels, and canals that are of fundamental military importance.
Legitimate communications targets include broadcasting and television stations, and telephone and telegraph exchanges of fundamental military importance.
Legitimate military-industrial targets include factories producing materiel (arms, transport, and communications equipment) for the military; metallurgical, engineering, and chemicals industries whose nature or purpose is essentially military; and the storage and transport installations serving such industries.
Legitimate military research targets include experimental research centers for the development of weapons and logistics.
Legitimate energy targets include installations providing energy mainly for national defense, such as coal and other fuels, and plants producing gas or electricity mainly for military consumption. Attacks on nuclear power stations and hydroelectric dams are generally, but not always, prohibited by the laws of war.
Note: Some of these may be civilian institutions, such as a university being used for academic research in peacetime being used for military research in time of war. Universities may be prime targets as a result. Factories making stereo equipment may be pressed into service for the manufacture of telecoms hardware.
