According to biographer John Eisenhower, the invasion of Mexico through Veracruz was "up to that time the most ambitious amphibious expedition in human history." The operation commenced on March 9, 1847 with the Siege of Veracruz, a joint army-navy operation led by Scott and Commodore David Conner. After safely landing his 12,000-man army, Scott encircled Veracruz and began bombarding it; the Mexican garrison surrendered on March 27. Seeking to avoid a mass uprising against the American invasion, Scott placed a priority on winning the cooperation of the Catholic Church. Among other initiatives designed to show respect for church property and officials, he ordered his men to salute Catholic priests on the streets of Veracruz. After securing supplies and wagons, Scott's army began the march towards Xalapa, a city on the way to Mexico City. Meanwhile, Polk dispatched Nicholas Trist, Secretary of State James Buchanan's chief clerk, to negotiate a peace treaty with Mexican leaders. Though they initially feuded, Scott and Trist eventually developed a strong working relationship.