In 1982, Israel decided to invade into Lebanon. in what was then called by the Israelis Operation Peace for Galilee, in order to root out Palestinian insurgents and support the Christian militias and the Free Lebanon State on the course of the Lebanese Civil War. Following the 1982-85 fighting, the IDF remained deployed in the area of southern Lebanon controlled by Lebanese Christian militias, which was declared by the Israelis as a security zone. Though most casualties on the course of consequent 1985-2000 conflict with Hezbollah were from the South Lebanon Army ranks, this deployment had claimed many casualties also from the IDF over the years. The most serious incident of IDF at the time being the helicopter disaster, which occurred on February 4, 1997 killing 73 soldiers from the Nahal Brigade, armored and Engineering fighters (188 Brigade and Battalion 601) and the helicopter crew.