sentences:  From the beginning, the objective of Morocco was to create a controlled and safe zone in the area considered as “useful” for its political and economic interests, that is, the Capital Al-Aaiun, the religious center Smara, and the phosphate field of Bu-Craa.In 1980 construction of the Sahara defensive walls began, consisting of every type of obstacle for infantry and armoured vehicles, such as mines and radars, all backed by Quick Intervention Units (Détachements d'Intervention Rapide) able to move to and quickly reinforce every location along the wall, aided by air-transport composed of Super Puma, AB-205 and CH-47 Chinook helicopters.As to the anti-tank defenses, it was decided additionally to use Aérospatiale SA 342 Gazelle helicopters with HOT missiles to neutralize the POLISARIO T-54, T-55 and BMP tanks.