Direct proof of use
The M1 Abrams was used by U.S. forces in the 2003 Iraq War during Operation Iraqi Freedom. Army University Press described the Abrams as playing a key role in the operation and tied the rapid seizure of Baghdad in 2003 to Iraqi forces' inability to counter highly mobile heavy armor in an urban environment.
A separate Army University Press case study of the Battle of Baghdad describes the U.S. 3rd Infantry Division's mechanized attacks into Baghdad in April 2003, including the 5 April reconnaissance-in-force and the larger 7 April Thunder Run that penetrated to the regime district and held it against Iraqi counterattacks. Washington Post reporting on the same operation identified the 7 April armored force as including M1A1 Abrams tanks and Bradley fighting vehicles from 3rd Infantry Division's 2nd Brigade.
Sources: The M1 Abrams Today and Tomorrow, The 2003 Battle of Baghdad, Washington Post Thunder Run Account
Timeline
On 3-4 April 2003, 3rd Infantry Division brigades attacked toward Baghdad International Airport and surrounded the city from the south, west, and north. On 5 April, the division commander ordered a Thunder Run to test whether the force could penetrate Baghdad's defenses with acceptable risk.
On 7 April 2003, 2nd Brigade's decisive Thunder Run entered western Baghdad after a predawn breach, pushed roughly twenty kilometers in two hours, seized the regime district, and fought through the day and night to retain the foothold. Army University Press later assessed that the Thunder Runs won the Battle of Baghdad and dislocated the Iraqi regime's control of the capital.
Sources: The 2003 Battle of Baghdad
Narrative
Abrams use in the 2003 campaign centered on U.S. armored maneuver and protected direct fire. In Baghdad, Abrams-equipped armored formations operated with Bradley fighting vehicles, artillery, air support, engineers, and logistics elements; the tank's role was part of a combined-arms operation rather than an isolated weapon effect.
The Baghdad fighting showed the Abrams in an urban assault role. The case study states that Iraqi planners did not expect U.S. tanks to be exposed to street fighting inside Baghdad, and that Iraqi defenses lacked the coordinated obstacles, artillery, and integrated kill zones needed to stop the mechanized formation.
After the initial seizure of Baghdad, Abrams tanks also remained relevant in the occupation and insurgency phase of the same war. Army University Press notes Abrams employment around Fallujah from late 2003 into spring 2004 for raids, cordon-and-search operations, overwatch, key-terrain security, and presence effects.
Sources: The 2003 Battle of Baghdad, The M1 Abrams Today and Tomorrow, Washington Post Thunder Run Account