The Iraqis used their Mi-25 helicopters, along with Gazelle helicopters armed with HOT missiles against columns of Iranian mechanised infantry and tanks. These "hunter-killer" teams of helicopters, which had been formed with the help of East German advisors, proved to be very costly for the Iranians. Aerial dogfights occurred between Iraqi MiG's and Iranian Phantom's. During this battle, the Iraqis also made first significant use of chemical weapons, contributing to their successes on the battlefield. During this instance, the Iraqis used large amounts of non-lethal tear gas to disrupt the offensive, throwing an entire attacking Iranian division into chaos.