 He participated in several major battles, including the Siege of Veracruz, the Battle of Molino del Rey, and the Battle for Mexico City.For gallant and meritorious conduct at Molino del Rey, he was brevetted to first lieutenant on September 8, 1847, receiving a promotion to the full rank in January 1848, when he was briefly assigned to duty in Pascagoula, Mississippi.Floyd-Jones was reassigned to a garrison in Detroit, Michigan, from 1848–50.