In the late 1970s, Mr. Walker retired from the Navy and became a private investigator. He often wore disguises and traveled the world collecting secret information and forwarding it to his buyers.

In August 1977, he traveled to Hong Kong to meet Mr. Whitworth, who was in port as a sailor on the aircraft carrier Constellation. Days later, Mr. Walker met with Soviet agents. Intelligence sources said at the time that the speed of the apparent exchanges suggested the Soviets regarded the information as highly valuable and timely.

“They were not doing that just to get something to research,” an intelligence source who requested anonymity told The New York Times in 1985. “They’re getting it because they want to use it immediately. They were clearly trying to mount a major effort to read United States communications. There’s no other reason to try to get that kind of access.”

John Anthony Walker Jr. was born on July 28, 1937, in Washington, the second of three sons. His father, John Sr., was a publicist for Warner Bros. who drank heavily. When the father’s career began failing, the Walkers moved to his hometown, Scranton, Pa. But John Sr. eventually left his wife and family, and John Jr. dropped out of his Catholic high school to enlist in the Navy. His family said he had joined after turning himself in for trying to burglarize a business.

As part of his plea deal in the spy case, Mr. Walker agreed to cooperate with investigators, in part to get his son a more lenient sentence. Michael Walker was sentenced to 25 years and released in 2000. John and Arthur Walker were given life sentences, and Mr. Whitworth was sentenced to 365 years.

Arthur Walker died in July in the same prison medical center where John Walker died. Complete information on John Walker’s survivors was not immediately available.

John and Arthur’s spy activities were reported to the authorities by John Walker’s former wife, Barbara Crowley, who said later that she had not realized that her son had also been involved. She and Mr. Walker divorced in the 1970s.