The Battle of Veracruz began on March 22, 1847. The day before, the squadron to which "Potomac" was assigned had shift to the command of Commodore Matthew Perry. On March 23, Perry ordered several naval units ashore to set up shore batteries. Parker was assigned to the shore battery from "Potomac" with all batteries under the overall command of Captain Alexander Slidell Mackenzie. The Army liaison officer to the Naval Shore Battery was Captain Robert E. Lee.