There, he served on the president's staff with the rank of major.
He served in the War of 1812 with the rank of adjutant.
After the war, he served as military aide, with the rank of colonel, to four governors from 1874 to 1883.
He served in the Union Army with the rank of first lieutenant in 1861.
Blackwill served in this position with the rank of Ambassador.
He served in the 2nd Foot Guards with the rank of lieutenant.
He served as judge advocate with the rank of major during the Civil War.
New surgeons were promoted to serving at the brigade level with the rank of Major.
From 1916 to 1918, he served as a field cashier with the temporary rank of Major.
He served in various staff positions during the war, with the rank of colonel of Volunteers.
