In 1913, while at Harvard, the New York Court of Appeals ruled that he was the legal heir of the $7,000,000 estate of Louis Carré Hamersley, his father's cousin who died in 1883. The will stipulated the bulk of his estate went to his male issue, or if there was none, to his cousin and his male descendants, but was appealed by several parties, including his cousin's late wife, Lily, who by then had married both George Spencer-Churchill, 8th Duke of Marlborough and Lord William Beresford before dying herself in 1909. Prior to his maturity, the Chemical National Bank managed the Hamersley estate. From 1937 to 1940, he served as president of the First Avenue Association and managed his large real estate empire out of 70 Pine Street in Manhattan. In 1914, Hamersley purchased the former John Armstrong Jr. estate in Dutchess County and erected a tudor revival mansion and gatehouse designed by Francis Hoppin. He expanded his estate, acquiring several farms to the north, and Maizeland on Cruger's Island in 1920, eventually owning what was described at one time as the second largest in Dutchess County. In 1926, he sold the combined estate to William B. Ward who immediately donated it to the Association for Improving the Condition of the Poor in memory of his father Robert. He also owned an estate at Sands Point on Long Island. In 1923, he had the family mansion at 1030 Fifth Avenue torn down and commissioned architects James Carpenter and Rosario Candela to build a modern apartment building on the site that featured a 23-room penthouse for Hamersley, which was completed in 1924.
Military career
After Harvard, Hamersley went to the Mexican border with Battery A of the Massachusetts National Guard, followed by a post as an ambulance driver for the American Field Service in France. While there, he attended the French Artillery School at Fontainebleau and, although the position of teaching horsemanship was offered to him, he joined the Sixth Field Artillery of the A.E.F's First Division as a lieutenant. He served in many engagements, and after the Armistice of 1918 was with the United States Army of Occupation in Germany for nine months. Hamersley later became a major in the Field Artillery Reserve and was a commander of the Jeff Heigl Post of the American Legion.
Sportsman
He was also a well-known speed boat pilot and, in 1925, he made a record run of 2 hours and 38 minutes from New York to Albany in his speedboat Cigarette Jr. In 1926, Cigarette IV won the first national speedboat regatta on the Potomac River and Hamersley received the President's Cup from President Calvin Coolidge. He also raced his schooner named Countess.
Personal life
In 1926, Hamersley was married to Hilles Morris, the daughter of Elizabeth Morris stock broker Stuyvesant Fish Morris Jr. and granddaughter Stuyvesant Fish Morris and Elly Morris. Together, they had residences in Southampton on Long Island, in Palm Beach in Florida, and at 1030 Fifth Avenue in Manhattan, and were the parents of one daughter and three sons:
Louis Gordon Hamersley Jr.
Stuyvesant Morris Hamersley
Hilles Elizabeth Hamersley
James Hooker Hamersley II, a writer, photographer and pilot.
After a brief illness, he died on June 2, 1942 at Southampton and was buried at Trinity Church Cemetery in Manhattan. After his death, his widow remarried, and was widowed from George Leslie Bartlett and Robert C. L. Timpson, managing partner of W.E. Hutton & Co.
