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.
In preparation for Operation Beit ol-Moqaddas, the Iranians had launched numerous air raids against Iraq air bases, destroying 47 jets (including Iraq's brand new Mirage F-1 fighter jets from France); this gave the Iranians air superiority over the battlefield while allowing them to monitor Iraqi troop movements.
On 29 April, Iran launched the offensive. 70,000 Revolutionary Guard and Basij members struck on several axes – Bostan, Susangerd, the west bank of the Karun River, and Ahvaz. The Basij launched human wave attacks, which were followed up by the regular army and Revolutionary Guard support along with tanks and helicopters.
In the early morning hours of 23 May 1982, the Iranians began the drive towards Khorramshahr across the Karun River. This part of Operation Beit ol-Moqaddas was spearheaded by the 77th Khorasan division with tanks along with the Revolutionary Guard and Basij.
The Iranians hit the Iraqis with destructive air strikes and massive artillery barrages, crossed the Karun River, captured bridgeheads, and launched human wave attacks towards the city. Saddam's defensive barricade collapsed; in less than 48 hours of fighting, the city fell and 19,000 Iraqis surrendered to the Iranians.
During Operation Muharram (1–21 November), the Iranians captured part of the Bayat oilfield with the help of their fighter jets and helicopters, destroying 105 Iraqi tanks, 70 APCs, and 7 planes with few losses. They nearly breached the Iraqi lines but failed to capture Mandali after the Iraqis sent reinforcements.