Chapman was born in New York to essayist John Jay Chapman and Minna Timmins (who died in 1898). He and his father moved to France soon after. His father re-married, to Elizabeth Chanler, a sister of William A. Chanler from the Astor family and Dudley–Winthrop family, when Chapman was a teenager.
When World War I broke out, his father and stepmother moved to London, England.
Harvard University.
In France, Chapman obtained dual-citizen status as a French and United States citizen. Chapman returned to the United States in his late teens to attend Harvard University. After graduating, Chapman returned to Europe, spending time in France and in Germany.
However, Chapman decided to stay in France, joining the French Foreign Legion on August 30, 1914, and served in the 3rd March regiment of the Legion.
He became friendly with four men during his days on the trenches: a Polish fighter who was known only as "Kohl", and Americans Alan Seeger, Henry Fansworth, and David King. The trio of Americans watched as Kohl was killed by a bullet while walking with his friends.
Chapman requested transfer to the Aéronautique Militaire, the army"s air arm. He attended flight school and was certified as a pilot.
Chapman flew many missions for the 1st Aviation Group and was commissioned a sergeant.
On June 17, 1916, he was flying over the Verdun sector when he was attacked by four German airplanes. During the engagement, Chapman suffered a head wound, most likely from an attack by then four-victory German flier Walter Höhndorf. Chapman landed his airplane safely, with Höhndorf getting his fifth victory as a result.
Prior to his last flight Chapman put loaded oranges onto his aircraft, intending to take these to Balsley who was in hospital recuperating from his wounds.
With Wintgens flying a Halberstadt Doctorate.II that day against Chapman"s Nieuport 16, Wintgens soon gained the upper hand. Chapman earned many medals and commendations during his military career.
Chapman earned many medals and commendations during his military career. Chapman was interested in the arts and in writing. He often found inspiration to write while he was in the middle of battles, and many of the letters he sent to his father were written in these circumstances. A book of these letters, called Letters from France, was published after his death. In his memory, the composer Charles Martin Loeffler, a friend of Chapman"s father, composed his quartet Music for Four Stringed Instruments. He was buried at the Meuse-Argonne American Cemetery and Memorial in France and a cenotaph in his honor was erected in Saint Matthew"s Episcopal Churchyard, Bedford, New New York
He was chosen as one of the founding members of North.124, the Escadrille Americane, also known as the Lafayette Escadrille.
