 Complete the following phrase:  In Washington, the regiment was assigned to construct fortifications and maintain a picket until March 1862, when they commenced a march with General George B. McClellans Peninsula campaign. Captain Clark, however, left the regiment in early April 1862, as he was appointed adjutant on the staff of his brother-in-law Brigadier General Joseph B. Plummer in the Army of the Mississippi. He arrived in time to participate at the 