His father's military service attracted him to the army, which had recently emerged from the War of 1812, and on August 10, 1818, he was commissioned as a surgeon's mate of the 1st Infantry.

The forty-three years that intervened before he became Surgeon General were filled largely with routine garrison duty, but included much field service in the wars of the period.

In 1831 he was ordered to Fort Howard, Wisconsin, and while on this duty he was detached for service as chief medical officer (with rank of major) of the forces operating under General Winfield Scott in the Black Hawk War of 1832.

By virtue of his rank he became medical director of this army commanded by General Zachary Taylor, but shortly after was sent north on account of sickness.

The years upon this detail largely involved work on examining boards and it was on this sort of duty that he was engaged when in 1861 he received the appointment to the office of Surgeon General.

Wood was son-in-law to former President Taylor and brother-in-law to Jefferson Davis and from his long duty in the War Department had many other influential friends.

But a new political party was now in control and President Abraham Lincoln chose Finley, the senior officer of the corps, for the coveted place on May 15, 1861.

The new Surgeon General was sixty-four at the time of appointment, but was in good physical condition and entered the office keen for the heavy duties devolving upon him.

It is difficult at this time to determine to what extent Finley influenced the policies and legislation affecting the medical department during his term of office.

From Boston he appealed against the treatment accorded him, but despite the efforts of influential friends no action could be obtained and hopeless of justice and redress he applied for admission to the retired list.