[3] Beginning in 1858, Ripley was a lieutenant in the Rutland Light Guards, a volunteer militia unit commanded by Horace Henry Baxter.

In May 1861 Ripley entered the Union Army for the Civil War as captain and commander of the Rutland Light Guards, which was mustered in as Company K, 1st Vermont Volunteer Infantry Regiment.

He served with the regiment in Washington, D.C. and Virginia during the entire three months of its service, including taking part in the Battle of Big Bethel.

[8] In August 1862 he was appointed commander of the 10th Vermont Infantry with the rank of colonel, but declined because of the physical disability caused by his wounds.

The militia had an active role providing patrols and security within the state and along the border with Canada, particularly following the October 1864 St. Albans Raid.

The citation reads: The President of the United States of America, in the name of Congress, takes pleasure in presenting the Medal of Honor to Lieutenant Colonel William Young Warren Ripley, United States Army, for extraordinary heroism on 1 July 1862, while serving with 1st U.S. Sharpshooters, in action at Malvern Hill, Virginia.

At a critical moment Lieutenant Colonel Ripley brought up two regiments, which he led against the enemy himself, being severely wounded.

He led some of the first troops to enter Richmond following the Lee's retreat, and warned Lincoln of a plot to assassinate him when he visited Virginia during the waning days of the war.