Ellsberg was born in New Haven, Connecticut, and grew up in Colorado. He was one of the very few Jews who were accepted into the United States Naval Academy, where he graduated with a Bachelor of Science degree in 1914. He subsequently earned his Master of Science degree from the Massachusetts Institute of Technology, in 1920. He received an honorary Eng.D. from University of Colorado at Boulder in 1929.

Ellsberg was commissioned in the Navy in 1914 and served on active duty until 1926. He became an expert in undersea salvage and rescue. In 1925, he raised the Navy submarine, S-51. For his efforts he was promoted to the rank of Commander by Act of Congress and given the Distinguished Service Medal by the Navy Department, since which time he has popularly been known as "Commander Ellsberg", regardless of his actual rank. Ellsberg described the raising of the S-51 in the book On the Bottom.

On June 1, 1918, Ellsberg married Lucy Buck Ellsberg. In letters to her he signed his name as "Ned". Their daughter Mary was born August 29, 1921.

After leaving active duty, Ellsberg worked for the Tide Water Oil Company and began writing books about his exploits and about historical events.

In December 1927, Ellsberg volunteered for active duty to rescue survivors trapped in the sunken submarine S-4. The rescue efforts failed and Ellsberg returned home in early January 1928.

Ellsberg's book Pigboats (1931) was the basis for the movie, Hell Below (1933), starring Robert Montgomery, Robert Young, Jimmy Durante, and Madge Evans.

Immediately after the Japanese attack on Pearl Harbor, Ellsberg rejoined the Navy. His first assignment was to conduct salvage operations at the newly liberated port of Massawa, then in Ethiopia - now Eritrea. Working in beastly heat with virtually no staff and poor administrative support, Ellsberg salvaged a large floating dry dock and the ships that had been sunk to block the harbor.

Ellsberg returned the port to operation and the ships salvaged were added to the Allies' merchant fleets. During his work in Massawa, Ellsberg reported to the Lend Lease coordinator in Cairo, Egypt, US Army Major General Russell Maxwell. Ellsberg renamed the S.S. Liebenfels, a large German freighter, salvaged and refitted at Massawa, the General Russell Maxwell. He described the salvage of the port of Massawa in his book Under the Red Sea Sun. Ellsberg was promoted to Captain by presidential order on June 19, 1942. The next year he was awarded the Legion of Merit by FDR in honor of his salvage efforts in Massawa.

In Under the Red Sea Sun, Ellsberg complained that the American contractor that was assigned to give him administrative support was very unhelpful, but he did not name that company. The company, Johnson, Drake & Piper, Inc., itself claimed credit for clearing the port in the privately printed book, "Middle East War Projects of Johnson, Drake & Piper, Inc., for the Corps of Engineers, U.S. Army, 1942-1943" (New York: Johnson, Drake & Piper, Inc., 1943). That book contains beautiful photographs and drawings showing projects around the Middle East.

From Massawa, Ellsberg went to North Africa to become Principal Salvage Officer in that theater. He worked under Admiral Andrew Cunningham, the British officer commanding naval forces in the area. Ellsberg's activities were detailed in No Banners, No Bugles.

Ellsberg, worn out from constant work, was ordered home in early 1943 to recuperate. After a time inspecting ship construction activities, Ellsberg was sent to England in time for the Normandy Invasion, where he was instrumental in preparing 89 damaged or superannuated ships for scuttling to make artificial harbors. This operation gained him great admiration in Britain where he was appointed an Officer of the Order of the British Empire (O.B.E.).

He remained on active duty after World War II rising to the rank of Rear Admiral before retiring in 1951 to enjoy Maine and Florida with his wife of sixty years. He continued to write, lecture and consult on engineering projects. He died in 1983 at the age of 91 and is buried in Willimantic, Connecticut.

Writing was a hobby for Ellsberg. He wrote many articles and reports. His books include:

• Captain Paul. (New York: Dodd, Mead, and Company, 1941)

• The Far Shore.(New York: Dodd, Mead, and Company, 1960)

• Hell on Ice: the Saga of the 'Jeannette'. (New York: Dodd, Mead, and Company, 1938)

• I Have Just Begun To Fight!' the Story of John Paul Jones. (New York: Dodd, Mead, and Company, 1942)

• On the Bottom. (New York: Dodd, Mead, and Company, 1929)

• Men Under the Sea. (New York: Dodd, Mead, and Company, 1939)

• Mid Watch, a Novel. (New York: Dodd, Mead, and Company, 1954)

• No Banners, No Bugles. (New York: Dodd, Mead, and Company, 1949)

• Ocean Gold. (New York: Dodd, Mead, and Company, 1935)

• Passport for Jennifer. (New York: Dodd, Mead, and Compney, 1952)

• Pigboats. (New York: Dodd, Mead, and Company, 1931)

• Report on Salvage Operations: Submarine S-51. (Washington: US GPO, 1927)

• Spanish Ingots. (New York: Dodd, Mead, and Company, 1936)

• S-54, Stories of the Sea. ( New York: Dodd, Mead, and Company, 1932)

• Thirty Fathoms Deep. (New York: Dodd, Mead, and Company, 1930)

• Treasure Below. (New York: Dodd, Mead, and Company, 1940)

• Under the Red Sea Sun. (New York: Dodd, Mead, and Company, 1946)