(də lông'), 1844–81, American arctic explorer, b. New York City, grad. Annapolis, 1865. In 1873 he was assigned to the Juniata, which was sent to the arctic to search for C. F. Hall's expedition on the Polaris. In 1879, backed by the younger James Gordon Bennett and under the auspices of the U.S. navy, he sailed from San Francisco on the U.S.S. Jeannette with a plan to penetrate Bering Strait and attempt a dash to the North Pole. There was then a theory that a current from Japan would speed them north through an open polar sea. However, there was no open sea, and the vessel was caught in the ice pack and drifted nearly two years until it was crushed and sank. The men had abandoned ship with provisions, sledges, and boats and now set out southward for Siberia. After reaching open water and embarking in the boats, they were separated. One boat was lost. A second, with De Long in command landed, but only two men sent ahead for aid survived. The third boat, commanded by George W. Melville, reached the Lena delta and was rescued. The next year Melville returned and found the bodies of De Long and his companions, who had perished from cold and hunger.
The expedition proved definitely that Wrangel Island was not the southern tip of a northern continent and had also proved essential facts about the polar drift. In traversing nearly 50,000 sq mi (129,500 sq km) of Arctic Ocean territory, De Long showed that the continental shelf of northern Siberia extends far northward and is dotted by numerous small islands. The expedition was also a demonstration of heroism. De Long's diary was edited by his widow as The Voyage of the Jeannette (1884). Melville's account was published as In the Lena Delta (1885).
- See E. Ellsberg, Hell on Ice (1938), a fictionalized account;.
- Explorer's Wife (1938);. ,
- A. Hoehling, The Jeannette Expedition (1967, repr. 1969);.
- In the Kingdom of Ice (2014). ,