After graduating from Harvard in 1855 and taking a course in civil engineering he went West and engaged in the preliminary surveys of the Iowa line of the Chicago & Rock Island Railway.

A company of artillery was organized and uniformed in Iowa and Hayes was elected its captain and was duly commissioned by Governor Kirkwood.

[2] As lieutenant colonel, Hayes commanded the regiment in the bloody Battle of Fredericksburg, being highly commended for his conduct.

The regiment made three successive charges on St. Mary's Heights, and more than one-half of its officers and men were killed or disabled.

[1] On the 1st of September, 1863, Hayes took command of the 1st Brigade, 1st Division, 5th Corps, which he held until the reorganization of the Army of the Potomac for the campaign of 1864.

[1][5] Hayes was commissioned brigadier general of volunteers from the May 12, 1864, and on recovering from his wound was assigned to the command of a brigade in Ayers's Division of the 5th Corps.

The Confederates made a desperate attempt to recapture this important communication to their base of supplies, attacking with thirteen brigades as reported, but were repulsed by General Hayes, who lost heavily, both his aid-de-camps, Lieutenants McKibbon (afterwards General Chambers McKibbon) and Perry being shot by his side.