The Iranians withdrew, leaving many destroyed and disabled tanks stuck in the mud, or, because of logistical misplanning, had run out of fuel and ammunition.

Iraq's invasion slowed drastically, and they became bogged down fighting Iranian paramilitary forces in urban actions such as the First Battle of Khorramshahr.

After the Islamic Revolution in 1979, the regular army and air force had suffered due to purges and lack of supplies and spare parts from their former Western allies, especially the US and UK, and was no longer the fifth most powerful military in the world.

A power struggle began within the new government in Tehran between President Abolhassan Banisadr and the opposition Islamic Republic Party (IRP), led by Prime Minister Mohammad-Ali Rajai.

It also led to an erosion of Banisadr's revolutionary credentials, as he was increasingly identified as defending and being part of a perceived secular, shah-era entity.

With declining support, President Banisadr convinced Supreme Leader Ayatollah Khomeini in Tehran (who had the final say in all state matters) to allow him to take personal command of the regular army.

After Banisadr took personal command and arrived at the front, he began planning a major offensive against the Iraqis, codenamed "Operation Nasr" (Victory).

The attack was to be carried out entirely by the regular army, and if successful would boost Banisadr's standing in the still chaotic Iranian political landscape, in addition to trumping the Pasdaran and their supporters.

Firstly, Iran's army having suffered disastrously during the revolution from purges and sanctions was simply unable to carry out proper combined arms operations.

All of the senior generals and entire swathes of the officer cadre from the Shah's era had been lost to purges (either executed, imprisoned, or fled abroad), and the remaining ones were not as well trained, and/or all too happy to embark on an operation to restore their credibility to the eyes of the regime.

While Banisadr had tried to alleviate some of the problems, and somewhat restored the Iranian army's command structure, it was simply not ready to carry out a major offensive.

The terrain around Susangerd was muddy and prone to seasonal flooding and rain turned the ground into a quagmire, the area was in many ways unsuitable for proper armored maneuver.

The distance the Iranian forces had to penetrate was also extremely lengthy, and it was easy for the Iraqis to counterattack and reinforce their troops, running counter to Iran's plan of achieving surprise.

A brigade of regular Iranian mountain troops attacked Iraqi forces that were in a defensive position, blocking the main highway between Tehran and Baghdad.

The second attack involved other Iranian mountain troops infiltrating towards occupied Mehran in a failed effort to liberate the town.

It involved an Iranian mechanized division attacking Iraqi forces west of the Karun River in the vicinity of Ahvaz.

Unknown to the Iranians, their plans had already begun to go awry when Iraqi observation aircraft spotted the column moving west towards Susangerd.

To make matters worse, Iraqi mechanized infantry with anti-tank weapons joined in, turning the battle into a slaughter for the Iranians.

Just when things were going badly, Iraqi aircraft also bombed the pontoon bridge across the Kharkeh River, trapping the Iranian tanks and preventing their retreat.

Meanwhile, during the débâcle at Susangerd, Iranian infantry forces at besieged Abadan attempted their breakout, in order to link up with the armored column.

Nevertheless, a centralized and inflexible Iraqi command and lack of foresight resulted in a failure to capitalize on their victory, which saved the Iranians from a total rout.

The Iraqis primarily dug in their tanks into the ground to act as static artillery, and while that worked at the fighting around Dezful and Susangerd, it meant that they were unable to follow up their victory and destroy the Iranians.

A minor Iraqi counterattack with helicopters and some armor was beaten back by Iranian forces near the town of Shush which lay just behind the Karkheh river on the line of advance to Dezful.

Many armored vehicles had been captured intact as they had been abandoned or stuck in the mud, and were put on display in Iraq (some were later even sold to Jordan, while others remained in storage until the 2003 invasion).

To make matters worse, with US-led sanctions on Iran, those tanks could not be replaced while the Iraqi ones could easily be (since they weren't under an embargo and had the support of the west).

By June 1981, things had gotten so bad for Banisadr that Iran's Parliament led by the IRP and Prime Minister Rajai impeached him.

Ayatollah Khomeini, who had played the role of a "neutral arbiter" and had through the past year had sought to settle the differences between Banisadr and his opponents, finally gave up on him, and approved his impeachment.

Banisadr was replaced by an unofficial junta, led by the now President Rajaii, the new Prime Minister Javad Bahonar, and the Speaker of Parliament Ali Akbar Hashemi Rafsanjani.

The Iranian regime unleashed their own wave of terror, torturing and executing over 3,000 members of the opposition, and purging the regular army once again.