Following a month of service at City Point, Virginia, the regiment remained at New York harbor until the end of the war.

After his unit was transferred to the American West in 1870, Lieutenant Coolidge was a member of Captain Rawn's command of ~25 regulars which opposed and stalled Chief Looking Glass' Nez Percé Indians at Lolo Pass.

Coolidge was promoted to Lieutenant Colonel of the Ninth Infantry Regiment on May 16, 1899, and he took part in the engagements at Zapote Bridge and Tarlac, Philippine Islands.

He assumed command following the death of Colonel Emerson H. Liscum during the Boxer Rebellion as part of the Allies relief of the Legation at Tianjin from June to July 1900.

In 1901 Coolidge was named Colonel of the Seventh Infantry Regiment, transferred to the Presidio of San Francisco, where he retired August 8, 1903, as a Brigadier General.

Brigadier General Charles Austin Coolidge died June 2, 1926, at Grace Hospital in Detroit, Michigan in his eighty-first year.

His grandfather Henry Rice was a member of the Boston City Council and was a Massachusetts state legislator.