The Iraqis, realising that the Iranians were planning to attack, decided to preempt them with Operation al-Fawz al-'Azim (Supreme Success) on 19 March. Using a large number of tanks, helicopters, and fighter jets, they attacked the Iranian buildup around the Roghabiyeh pass. Though Saddam and his generals assumed they had succeeded, in reality the Iranian forces remained fully intact.
Iran's next major offensive, led by then Colonel Ali Sayad Shirazi , was Operation Fath-ol-Mobeen (Undeniable Victory). On 22 March 1982, Iran launched an attack which took the Iraqi forces by surprise: using Chinook helicopters, they landed behind Iraqi lines, silenced their artillery, and captured an Iraqi headquarters. The Iranian Basij then launched "human wave" attacks, consisting of 1,000 fighters per wave. Though they took heavy losses, they eventually broke through Iraqi lines. Operation Undeniable Victory was an Iranian victory; Iraqi forces were driven away from Shush, Dezful and Ahvaz. The Iranian armed forces destroyed 320–400 Iraqi tanks and armored vehicles in a costly success.