Iran may have prevented a quick Iraqi victory by a rapid mobilization of volunteers and deployment of loyal Pasdaran forces to the front. Besides enlisting the Iranian pilots, the new revolutionary regime also recalled veterans of the old imperial army, although many experienced officers, most of whom had been trained in the United States, had been purged. Furthermore, the Pasdaran and Basij (what Khomeini called the "Army of Twenty Million" or People's Militia) recruited at least 100,000 volunteers. Approximately 200,000 soldiers were sent to the front by the end of November 1980. They were ideologically committed troops (some members even carried their own shrouds to the front in the expectation of martyrdom) that fought bravely despite inadequate armor support. For example, on November 7 commando units played a significant role, with the navy and air force, in an assault on Iraqi oil export terminals at Mina al Bakr and Al Faw. Iran hoped to diminish Iraq's financial resources by reducing its oil revenues. Iran also attacked the northern pipeline in the early days of the war and persuaded Syria to close the Iraqi pipeline that crossed its territory.

Iran's resistance at the outset of the Iraqi invasion was unexpectedly strong, but it was neither well organized nor equally successful on all fronts. Iraq easily advanced in the northern and central sections and crushed the Pasdaran's scattered resistance there. Iraqi troops, however, faced untiring resistance in Khuzestan. President Saddam Husayn of Iraq may have thought that the approximately 3 million Arabs of Khuzestan would join the Iraqis against Tehran. Instead, many allied with Iran's regular and irregular armed forces and fought in the battles at Dezful, Khorramshahr, and Abadan. Soon after capturing Khorramshahr, the Iraqi troops lost their initiative and began to dig in along their line of advance.

Data as of December 1987