The Mexican Army dislocated the monks living here during the Mexican-American War in order to defend Mexico City from the invading U.S. Army. The Mexicans fortified the building, which included building the parapet. At the time, the complex was far outside the city limits. On 20 August 1847, Battle of Churubusco was fought. When the Mexicans ran out of ammunition, the battle turned to hand-to-hand fighting. When the Mexicans were defeated U.S. General David Twiggs asked General Pedro María de Anaya to surrender his ammunition. The reported response of Anaya is "If there was any, you wouldn't be here." This was also the last stand of Saint Patrick's Battalion, a regiment of mostly Irish defectors from the U.S. army. A plaque honoring them is placed at the main entrance. In 1869, President Benito Juárez declared the site a national monument in honor of the battle, which was reaffirmed in 1933. However, this did not turn it into a museum. From 1876 to 1914, it served as a military hospital, specializing in contagious diseases. In the 1920s, it was an art school, and from 1920 to 1960 it was a depot. In the 1960s and 1970s, this building was known unofficially as the Transport Museum as a large number of old vehicles were stored there. This collection was eventually sent to Zacatecas in 1985.