[1] His father William R. Harmon fought in the Civil War with the 70th Ohio Volunteers and later served as an officer with the "Buffalo Soldiers".

William had determined that there was money to be made by providing a way by which people interested in owning a home could purchase one in installments, making a small down payment and paying what they could monthly.

Further developments were soon built in Ohio and western Pennsylvania, followed by expansion into various cities in the Midwest and the East Coast of the United States.

Wood, Harmon & Co. also diversified by creating other companies to acquire and hold business properties and real estate for lease and/or sale.

In 1908 he learned to fly in approximately one week, and was awarded the sixth pilot's license issued in the United States.

[10] In September 1909 he was the subject of a large search when he flew solo over western Massachusetts and lost contact with those on the ground; Harmon landed safely and returned to city via car and train.

[14][15] In March 1910 he attempted a balloon flight from San Antonio, Texas to New York, but was brought down early by weather.

Later in July Harmon made an attempt to fly across the Long Island Sound, but crashed when his Farman III biplane lost power; he was not seriously injured.

[22] In December 1911 he announced retirement from balloon racing and airplanes at the behest of his wife, father-in-law, and various business associates.

[24] In April 1915 he, along with several other aviators and wealthy friends, participated in a scheme to commute regularly from New York to points at the eastern end of Long Island by airplane.

In June, Harmon installed a plaque commemorating Lindbergh at Le Bourget airport in Paris.

In 1912 Harmon was part of a syndicate that purchased Oklahoma oil leases from Charles Page for $1.25 million dollars.

[38] On April 22, 1918, Harmon enlisted in the NY Guard Service, Troop A, Squadron A; he was discharged June 12, 1918.

On October 13, 1918, he was commissioned as a captain in Air Signal Corps and served in France from November 1918 to January 1919, training aviators.

He met Madeline Keltie, an opera singer 24 years his junior, in 1924 at the American embassy in Rome, Italy.

He resided in Cannes during the Nazi occupation in World War II, but due to his condition German forces did not pursue internment or other confinement.

[26][45] He was interred the Rhone American Cemetery and Memorial, Draguignan, Departement du Var, Provence-Alpes-Côte d'Azur, France.