William was born on 24 March 1843, in Chichester, New Hampshire, where his father was a wheelwright.

Bill enlisted in the Union Army in May 1861 at the age of 19 and was assigned to Company I of the 2nd New Hampshire Infantry.

This unit was formed in Baltimore, Maryland, on 15 July 1863, and William Appleton joined Company H as a second lieutenant in August that same year.

Citation: The first man of the Eighteenth Corps to enter the enemy's works at Petersburg, Va., 15 June 1864.

Valiant service in a desperate assault at New Market Heights, Va., inspiring the Union troops by his example of steady courage.