On 5 January 1981, Iran had reorganised its forces enough to launch a large-scale offensive, Operation Nasr (Victory). The Iranians launched their major armoured offensive from Dezful in the direction of Susangerd, consisting of tank brigades from the 16th "Qazvin", 77th "Khorasan", and 92nd Khuzestan Armoured Divisions, and broke through Iraqi lines. However, the Iranian tanks had raced through Iraqi lines with their flanks unprotected and with no infantry support; as a result, they were cut off by Iraqi tanks. In the ensuing Battle of Dezful, the Iranian armoured divisions were nearly wiped out in one of the biggest tank battles of the war. When the Iranian tanks tried to manoeuvre, they became stuck in the mud of the marshes, and many tanks were abandoned. The Iraqis lost 45 T-55 and T-62 tanks, while the Iranians lost 100–200 Chieftain and M-60 tanks. Reporters counted roughly 150 destroyed or deserted Iranian tanks, and also 40 Iraqi tanks. 141 Iranians were killed during the battle.