War with Mexico having been declared, General Taylor's army became an army of invasion. Volunteers for the war now began coming from the States. In August the movement on Monterey began, and on the 19th of September, Taylor's army was encamped before the city. The battle of Monterey was begun on the 21st, and the desperately defended city was surrendered and evacuated on the 24th. Grant, although then doing quartermaster's duty, having his station with the baggage train, went to the front on the first day, and was a participant in the assault, incurring all its perils, and volunteering for the extremely hazardous duty of a messenger between different parts of the force. When General Scott arrived at the mouth of the Rio Grande, Grant's regiment was detached from Taylor's army and joined Scott's. He was present and participated in the siege of Vera Cruz, the battle of Cerro Gordo, the assault on Churubusco, the storming of Chapultepec, for which he volunteered with a part of his company, and the battle of Molino del Rey. Colonel Garland, commander of the brigade, in his report of the storming of Chapultepec, said: "Lieutenant Grant, 4th Infantry, acquitted himself most nobly upon several occasions under my own observation." After the battle of Molino del Rey he was appointed on the field a first lieutenant for his gallantry. For his conduct at Chapultepec he was later brevetted a captain, to date from that battle, September 13, 1847. He entered the city of Mexico a first lieutenant, after having been, as he says, in all the engagements of the war possible for any one man, in a regiment that lost more officers during the war than it ever had present in a single engagement. Perhaps his most notable exploit was during the assault on the gate of San Cosme, under command of General Worth. While reconnoitring for position, Grant observed a church not far away, having a belfry. With another officer and a howitzer, and men to work it, he reached the church, and, by dismounting the gun, carried it to the belfry, where it was mounted again but a few hundred yards from San Cosme, and did excellent service. General Worth sent Lieutenant Pemberton (the same who in the civil war defended Vicksburg) to bring Grant to him. The general complimented Lieutenant Grant on the execution his gun was doing, and ordered a captain of voltigeurs to report to him with another gun. "I could not tell the general," says Grant, "that there was not room enough in the steeple for another gun, because he probably would have looked upon such a statement as a contradiction from a second lieutenant. I took the captain with me, but did not use his gun."