The first attack (April 24 to May 12) consisted of 70,000 Pasdaran (members of Iran's military, the (Islamic Revolutionary Guard Corps IRGC) and succeeded in pushing the Iraqis out of the Ahvaz-Susangerd area.
The Iraqis withdrew back to Khorramshahr city and, on May 20th, launched a counter attack against the Iranians, which was repulsed.
The Iranians then launched an all out assault on Khorramshahr, capturing two of the defense lines in the Pol-e No and Shalamcheh region.
The Iranians gathered around the Shatt al-Arab (known as Arvand Rud in Iran) waterway, surrounding the city and, thus, beginning the second siege. The Iranians finally recaptured the city on May 24th after two days of bitter fighting.