Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 8. Definition of Military Objectives
Section A. General
The UK LOAC Pamphlet (1981) states that military objectives are:
objects which by their location, nature, 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. They include buildings, minefields, weapons, concentrations of troops and individual enemy combatants. 
United Kingdom, The Law of Armed Conflict, D/DAT/13/35/66, Army Code 71130 (Revised 1981), Ministry of Defence, prepared under the Direction of The Chief of the General Staff, 1981, Section 4, p. 13, § 3(b)(2).
The UK LOAC Manual (2004) states:
5.4.1. The term “military objective” includes combatant members of the enemy armed forces and their military weapons, vehicles, equipment and installations. It may include other objects which have military value such as bridges, communications towers, electricity and refined oil production facilities. Objects are only military objectives if they come within the following definition:
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.
5.4.4. The definition of military objectives contains various elements that require explanation:
a. The second part of the definition limits the first. Both parts must apply before an object can be considered a military objective.
b. Attacks on military objectives that cause incidental loss or damage to civilians are not prohibited so long as the proportionality rule is complied with.
c. “Nature” refers to the type of object, for example, military transports, command and control centres or communications stations.
d. “Location” includes areas which are militarily important because they must be captured or denied to the enemy or because the enemy must be made to retreat from them. An area of land can, thus, be a military objective.
e. “Purpose” means the future intended use of an object while “use” means its present function.
f. The words “nature, location, purpose or use” seem at first sight to allow a wide discretion, but they are subject to the qualifications later in the definition of “effective contribution to military action” and the offering of “a definite military advantage”. There does not have to be geographical proximity between “effective contribution” and “military advantage”. That means that attacks on military supply dumps in the rear or diversionary attacks, away from the area of actual military operations, can be launched.
g. “Military action” means military action generally, not a limited or specific military operation.
h. The words “in the circumstances ruling at the time” are important. If, for example, the enemy moved a divisional headquarters into a disused textile factory, an attack on that headquarters would be permissible (even though the factory might be destroyed in the process) because of the prevailing circumstances. Once the enemy moved their headquarters away, the circumstances would change again and the immunity of the factory would be restored.
i. “Definite” means a concrete and perceptible military advantage rather than a hypothetical and speculative one.
j. “Military advantage”. The military advantage anticipated from an attack refers to the advantage anticipated from the attack considered as a whole and not only from isolated or particular parts of the attack. The advantage need not be immediate. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 5.4.1 and 5.4.4.
The manual further states:
Unless they are exempt from attack under paragraphs 13.35 [relating to hospital ships] or 12.29 [relating to conditions of exemption for medical aircraft], enemy warships and military aircraft and enemy auxiliary vessels and aircraft are military objectives. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 12.39.
With regard to non-international armed conflict, the manual states:
There is no definition of military objectives or attacks in the treaty law dealing with non-international armed conflicts. Nevertheless, the definitions used in respect of international armed conflicts should be treated as applicable. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.9.1.
In 2003, during a debate in the House of Commons, the UK Secretary of State for Defence stated:
On the bombing campaign in Baghdad, I anticipate that the great majority of people there will see for themselves the nature of the targeting. It will be clear that regime targets – Saddam’s Ministries and palaces – are being destroyed. As the campaign evolves, there will be no clearer message to the people of Iraq that we have no quarrel with them, but that we do have a serious difference with Saddam Hussein. 
United Kingdom, House of Commons, Statement by the Secretary of State for Defence, Hansard, 21 March 2003, Vol. 401, Debates, cols. 1217–1218.
In 1991, in a report submitted to the UN Security Council on operations in the Gulf War, the United Kingdom stated: “Operations by United Kingdom forces have involved aerial attacks on Iraqi installations supporting Iraq’s capacity to sustain its illegal occupation of Kuwait.” 
United Kingdom, Letter dated 21 January 1991 to the President of the UN Security Council, UN Doc. S/22115, 21 January 1991.