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Units of Iraq's 1st Corps spent two months in their trenches waiting for the Iranians to attack. The offensive came on 19 October 1983 as the Iranians and Peshmerga guerrillas of the Patriotic Union of Kurdistan took 250 square miles (650 km2) of territory. This included a number of Kurdish villages and exerted a significant amount of pressure on Penjwin.
The focus of the fourth Dawn operation in September 1983 was the northern sector in Iranian Kurdistan. Three Iranian regular divisions, the Revolutionary Guard, and Kurdistan Democratic Party (KDP) elements amassed in Marivan and Sardasht in a move to threaten the major Iraqi city Suleimaniyah. Iran's strategy was to press Kurdish tribes to occupy the Banjuin Valley, which was within 45 km (28 mi) of Suleimaniyah and 140 km (87 mi) from the oilfields of Kirkuk. To stem the tide, Iraq deployed Mi-8 attack helicopters equipped with chemical weapons and executed 120 sorties against the Iranian force, which stopped them 15 km (9.3 mi) into Iraqi territory. 5,000 Iranians and 18,000 Iraqis were killed & wounded.
Iran gained 110 km² (42 sq mi) of its territory back in the north, gained 15 km² (5.8 sq mi) of Iraqi land, and captured 785 Iraqi prisoners while Iraq abandoned large quantities of valuable weapons and war materiel in the field. Iraq responded to these losses by firing a series of SCUD-B missiles into the cities of Dezful, Masjid Suleiman, and Behbehan, while the Iraqi naval aircraft mined the port of Bandar Khomeini. Iran's use of artillery against Basra while the battles in the north raged created multiple fronts, which effectively confused and wore down Iraq.
The attack was successful but the Iranians suffered high casualties due to Iraqi gas attacks. Unlike other operations and battles of the Iran–Iraq War, environmental conditions and operative restrictions were of high significance for this operation. Also the military medicine organization of the Pasdaran was important in this battle; they used special methods to save the wounded and carried out rescue operations.
However, in response to this victory, the Iraqis launched the first Scud missiles into Iran, hitting six cities.