Règle correspondante
Spain
Practice Relating to Rule 8. Definition of Military Objectives
Section A. General
Spain’s LOAC Manual (1996) states:
4.2.b. … military objectives are … objects which by their nature, location, purpose or use make an effective contribution to military action or whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage.
4.2.b.(2) … insofar as objects are concerned, there can only be considered military objectives those objects which by their nature, location, purpose or use make an effective contribution to military action or whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a clear military advantage. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Publicación OR7-004, 2 Tomos, aprobado por el Estado Mayor del Ejército, División de Operaciones, 18 March 1996, Vol. I, §§ 4.2.b and 4.2.b.(2).
Spain’s LOAC Manual (2007) states:
Military objectives are 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. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 1.3.b.(1); see also § 4.2.b.(1).
In defining “definite military advantage”, the manual states: “‘Definite military advantage’ means a concrete advantage. It is not therefore lawful to launch attacks that only make indirect contributions or offer possible advantages.” 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 4.2.b.
The manual further states: “A target can only be considered a military objective when sufficient information has been obtained to dispel any doubts and establish reasonable certainty about its nature, based on the facts available at that time.” 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 4.4.a.
The manual also states: “The principle of military necessity is implicit in the definition of military objectives.” 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 2.4.c.(6).
Upon ratification of the 1977 Additional Protocol I, Spain stated with respect to Articles 51, 52 and 57 of the Protocol:
It is the understanding [of the Spanish Government] that the “military advantage” which these articles mention refers to the advantage expected from the attack as a whole and not from isolated parts of it. 
Spain, Interpretative declarations made upon ratification of the 1977 Additional Protocol I, 21 April 1989, § 6.