In September 1847, an Army operation to seize and destroy a weapons manufacturing site and munitions storage area in hostile enemy territory results in a brief but heated battle that secures the outermost defenses of the enemyAca,!a,,cs capital.

Defeated at the battles of Contreras and Churubusco on August 20, 1847, the retreating Mexican army established defensive positions around Mexico City. American General Winfield Scott and Mexican General Antonio Lopez de Santa Anna concluded an armistice, hoping that an end to the war could be arranged. Negotiations between the two sides produced no results. Santa Anna had gained time, though, to prepare and strengthen the cityAca,!a,,cs defenses in violation of the armisticeAca,!a,,cs terms. Scott warned Santa Anna regarding the violations and rescinded the armistice on September 7.

The best approaches for attacking Mexico City were from the south and west sides through city gates or Aca,!A"garitas.Aca,!A? These could only be reached via causeways spanning impassable marshes. The two western causeways were defended by Chapultepec Castle, located on a hill southwest of the city. West of Chapultepec were the massive stone walls of el Molino del Rey (the KingAca,!a,,cs Mill) and the nearby earthwork fort, Casa Mata. Scott was informed that el Molino del Rey housed a cannon foundry and Casa Mata held a large supply of gunpowder. Intelligence reports indicated that many church bells were being sent there for melting and casting into cannon. Scott determined to drive out enemy forces occupying the buildings, destroy the foundry, and seize the gunpowder. He recognized the strategic importance of destroying the weapons manufacturing capabilities and the munitions in order to reduce the enemyAca,!a,,cs ability to continue waging war.

The mission was entrusted to ScottAca,!a,,cs two most combat-tested divisions. General William J. WorthAca,!a,,cs reinforced division that included dragoons (mounted soldiers) and artillery fire support was to attack at dawn on September 8. General David TwiggsAca,!a,,c reinforced division was to feign attacking the city from the south as a diversion. After a brief artillery bombardment the Americans advanced. Mexican artillery and small arms opened a withering fire, making it apparent the defenders were much stronger than previously thought. An anticipated skirmish became a fierce, hard-fought battle. An ad-hoc 500-man storming party, or Aca,!A"forlorn hope,Aca,!A? briefly overran the Mexican infantry and artillery positions outside the Molino but were repelled by a counterattack. Eleven out of fourteen officers in the party, including the officer in charge, were killed. American artillery fire and aggressive attacks on the Molino from the east forced the Mexicans from the structure and it fell into American hands. The attack on Casa Mata also involved heavy fighting. American artillery fire supported this attack as well. Again, heavy enemy fire and a strong counterattack caused heavy American casualties. However, the Mexicans there lacked artillery and were forced to retreat as heavy artillery fire battered them. A potentially disastrous Mexican cavalry strike against the American flank was discouraged by artillery fire and a spirited demonstration by the dragoons. Throughout the battle, the superior employment of combined arms by American forces made the difference between victory and defeat.

The battle lasted approximately two hours. No cannon foundry was found; only a few gun molds, but no cannon. The mill buildings were ordered destroyed. Casa Mata, which caught on fire sometime during or right after the battle, blew up, injuring several American soldiers. The Mexicans lost three artillery pieces; of greater importance, however, was that many enemy soldiers became prisoners of war and the Mexican armyAca,!a,,cs morale sank even lower, just at the time it was needed most to defend its capital city. That defense would fail. Six days after the fall of Molino del Rey and Casa Mata, the victorious American forces captured Mexico City itself.