After the Iraqi offensive stalled in March 1981, there was little change in the front other than Iran retaking the high ground above Susangerd in May. By late 1981, Iran returned to the offensive and launched a new operation (Operation Samen-ol-A'emeh (The Eighth Imam)), ending the Iraqi Siege of Abadan on 27–29 September 1981. The Iranians used a combined force of regular army artillery with small groups of armor, supported by Pasdaran (IRGC) and Basij infantry. On 15 October, after breaking the siege, a large Iranian convoy was ambushed by Iraqi tanks, and during the ensuing tank battle Iran lost 20 Chieftains and other armored vehicles and withdrew from the previously gained territory.