He served as a lieutenant in the
United States Navy in the
South West Pacific theatre during World War II. Gardiner worked on
Wall Street, for the Empire Trust Company and owned a 42-acre shopping center in
Islip, New York. In 1937 he became a member of the New Hampshire
Society of the Cincinnati.
Gardiner family properties He and his sister
Alexandra Gardiner Creel inherited
Gardiner's Island from their aunt, Sarah Diodati Gardiner, when she died in 1953. Gardiner had long-running disputes with his sister, and her daughter,
Alexandra Creel Goelet. Goelet and her husband were conservationists, while Gardiner was an enthusiastic hunter. From 1953, when Gardiner and his sister inherited the Island, until 1977, the Island's operating costs had been covered by a trust set up by the aunt from whom they inherited the property. Due to their disputes, Gardiner refused to contribute to the taxes and other costs of maintaining the property–which, at that time, were more than $1 million per year. He didn't contribute for over a decade. They, in turn, went to court to bar him from visiting the property. In 1971, Representative
Otis Pike proposed a bill to expropriate
Gardiners Island, to turn it into a Federal National Monument. Gardiner complained that the proposal to expropriate his family's property was unfair, when the
Rockefeller family had been allowed to continue to own their
Pocantico Hills estate. Gardiner inherited
Sagtikos Manor, a 10-acre heritage property on Long Island. Gardiner inherited the property, which had been in his family since the 18th century, in the 1930s. Gardiner and his wife Eunice used the property as their primary residence for several years, early in their marriage. In 1963, when the
Sagtikos Manor Historical Society was founded, the Gardiners stopped using it as their primary residence, let the Historical Society use part of the structure, but insisted the Historical Society reserve a suite for him. The property was placed on the
National Register of Historic Places in the 1970s. In 1986, Gardiner transferred ownership of the property to the nonprofit Robert David Lion Gardiner Foundation. Today, Sagtikos Manor stands as a small museum rich in historical value to the
American Revolution and its era onward. ==Personal life==