Iran–Iraq War
Iranian military preparations

In Iran, severe officer purges, including numerous executions ordered by Sadegh Khalkhali, the new Revolutionary Court judge, and shortages of spare parts for Iran's American and British-made equipment had crippled Iran's once-mighty military. Between February and September 1979, Iran's government executed 85 senior generals and forced all major-generals and most brigadier-generals into early retirement.

By September 1980, the revolutionary government had purged some 12,000 officers of all levels from the army. These purges resulted in a drastic decline in the Iranian military's operational capacities.

On the eve of the revolution in 1978, international experts in military science had assessed that Iran's armed forces were the fifth most powerful in the world. However, by the eve of war with Iraq, the recently formidable Iranian army was in many crucial ways a shell of its former self, having been badly weakened by losses in experienced personnel. The desertion rate had reached 60%, the officer corps was devastated and its most highly skilled soldiers and aviators had been exiled, imprisoned, or executed. When the invasion occurred, many pilots and officers were released from prison, or had their executions commuted to combat the Iraqis. Throughout the war, Iran never managed to fully recover from this flight of human capital.

Many junior officers were promoted to generals, resulting in the army being more integrated as a part of the regime by the war's end. Meanwhile, a new paramilitary organisation gained prominence in Iran, the Islamic Revolutionary Guard Corps. Created to protect the new regime and serve as a counterbalance to the army, the Revolutionary Guards (IRGC) had been trained to act only as a militia and struggled to adapt as needed following the Iraqi invasion, initially refusing to fight alongside the regular army, resulting in many defeats. It was not until 1982 that the two groups began carrying out combined operations.

An additional paramilitary militia was founded in response to the invasion, the "Army of 20 Million", commonly known as the Basij. The Basij were poorly armed and had members as young as 12 and as old as 70. They often acted in conjunction with the Revolutionary Guard, launching so-called human wave attacks and other campaigns against the Iraqis. They were subordinate to the Revolutionary Guards, and they made up most of the manpower that was used in the Revolutionary Guard's attacks.

Stephen Pelletiere wrote in his 1992 book The Iran–Iraq War: Chaos in a Vacuum:

The human wave has been largely misconstrued both by the popular media in the West and by many scholars. The Iranians did not merely assemble masses of individuals, point them at the enemy, and order a charge. The waves were made up of the 22-man squads mentioned above. Each squad was assigned a specific objective. In battle, they would surge forward to accomplish their missions, and thus gave the impression of a human wave pouring against enemy lines.

Despite neglect by the new regime, at the outset of the conflict, Iran still had at least 1,000 operational tanks and several hundred functional aircraft and could cannibalize equipment to procure spare parts. Continuous sanctions greatly limited Iran from acquiring many additional heavy weapons, including tanks and aircraft.
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