Related Rule
Practice Relating to Rule 8. Definition of Military Objectives
Section C. Places where armed forces or their materiel are located
The Military Manual (1993) of the Netherlands considers that positions of military units, such as artillery positions, constitute military objectives “under all circumstances”. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. V-3.
The Military Manual (2005) of the Netherlands states:
Naturally, locations of military units also form military objectives, e.g., artillery and guided-weapon positions. Mention must also be made of military aircraft, air bases, communication and radar installations, and storage sites of military equipment. All these objects constitute military objectives, in all circumstances. Whether a road or railway line forms a military objective depends on the military situation in the field. The answer to the question whether neutralization of such an object at that time confers military advantage is decisive to the object’s classification. This applies even more strictly to objects which, by nature, are intended for civilian purposes (e.g. houses and school buildings). However, these may become military objectives by virtue of their use (e.g. as military billets and equipment as command posts). 