Related Rule
Spain
Practice Relating to Rule 12. Definition of Indiscriminate Attacks
Section B. Attacks which cannot be directed at a specific military objective
Spain’s LOAC Manual (1996) states:
Indiscriminate military objectives are those in which military objects and civilian and civil objects cannot be distinguished and therefore attacking them will cause civilian damages excessive in relation to the direct military advantage anticipated. Indiscriminate attacks are prohibited. Indiscriminate attacks are those:
- which employ a method or means which cannot be directed at a specific military objective. 
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, § 4.4.c.
Spain’s LOAC Manual (2007) includes in its definition of indiscriminate attacks “attacks that employ a method or means of combat which cannot be directed at a specific military objective”. 
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.c.