When Saddam Hussein decided to invade Iran in 1980 (starting of the longest traditional war of the 20th century), the time for the attack was no coincidence. Iran’s military power had been weakened significantly during the recent revolution, with many of its leaders falling victim to the ongoing purges. The country was also under US sanctions making it difficult to repair and re-stock their equipment, and it was still divided by internal power-struggles. All of this made a counter attack (Operation Nasr) extremely difficult to organize.
There was so much chaos, that it took the Iranian forces over three months to answer this threat, by deploying their military in the region. Not to say the Iraqi forces would have had it easy… After the initial success the invasion stalled quickly, thanks to the various paramilitary forces and irregulars engaging them, while the Iranian Air Force and Navy (acting separately from the Army) basically shredded their Iraqi counterparts right in the beginning.
Operation Nasr was the first combined arms operation launched on land against the Iraqi invaders. It consisted of an impressive 300 tanks (mainly M-47s, M-60 Patton’s and British Chieftains), supported by infantry and helicopters. While the Iranian forces had the advantage in numbers, there were several factors working against them… They lacked experienced military leadership thanks to the ongoing post-revolutionary purges, they lacked proper reconnaissance, and worst of all, they really did choose a poor spot for a massive armored engagement. The region around Dezful was an ocean of mud thanks to the seasonal weather, so the Iranian forces would be confined to the paved roads moving in columns, or face getting stuck in the open.
The operation was launched beginning of 1981, and thanks to their observation aircraft the Iraqi forces spotted the advancing armored columns well in advance. They decided to dig their tanks (mostly Soviet T-62s and T-55s) into a hull down position in front of- and to the sides of the Iranian advance, setting a trap. Digging their tanks in was often used by the Iraqi military and it certainly worked this time, as they did not give up much mobility for the increased protection in the muddy conditions.
After crossing the Karkheh River via pontoon bridges the day before, the Iranian forces made contact on the 6th of January. Due to their lack of reconnaissance they moved right into the Iraqi trap. As the first armored column came under heavy fire simultaneously from the front and both sides, they first did try to break through in an armored spearhead, but suffered heavy losses. As this failed they did try to maneuver, but got stuck in the mud as soon as they drove off the paved road. The first armored column was quickly decimated, but the Iranian forces did not give up.
The second armored column moved forward as well and did try to power its way through with the help of Iranian AH-1J Seacobra helicopters. These did actually destroy several Iraqi tanks (they were stationary targets after all), but not enough to break the attack. The Iraqi forces did reply by bringing in their own fighter jets and attack helicopters, who took on the enemy air force and also bombed the Iranian pontoon bridges. This did not only make a retreat impossible, but also kept the Iranian infantry out of the fight completely, as they got stuck on the other side of the river. By bringing in additional mechanized infantry with anti-tank weapons as well against the (now also stuck) second armored division, the ambush turned into a slaughter.
The battle raged on for days in a chaos of mud and steel, when the Iranian engineers finally managed to repair the bridge, allowing a retreat. Being in dug in positions the Iraqi forces could not pursue them. As the battle died down, most of the first two Iranian armored columns did lay in the mud, either destroyed or abandoned, marking an important victory for the invaders in this 5 day engagement. As usual, the numbers are ranging wildly depending on which side recorded them, but most sources agree that Iraq destroyed or captured around 150 tanks, while only losing about 50 of their own. The captured tanks (many of them Chieftains) were partially used by their own military in the coming years and partially sold onto Jordan. After this episode, the war raged on for many more years until 1988, but never again did the two sides have a tank battle of this magnitude.