Walker was sentenced to life in prison after pleading guilty in 1985 to passing secrets to the Soviets while he was a shipboard communications officer.
The security breach was then considered among the largest and most devastating leaks of military secrets in the nation's history.
A cryptologist, Walker used his high-level security clearance to provide Navy codes, ship locations, and other sensitive data in exchange for cash. After his 1976 retirement, Walker recruited his son, his brother and a friend to keep providing the Soviets fresh information. All were convicted.
Walker's spying career began in 1967, when he was based at the massive U.S. Naval Station in Norfolk, Virginia. Walker went to the Soviet Embassy in Washington and volunteered to hand over secret coded material on a regular basis, according to court documents.
Over the next 17 years, the Soviets used the information provided by Walker and his accomplices to decode millions of secret U.S. Navy messages and to learn about the tactics the Americans deployed against them.
After his arrest, prosecutors said Walker's betrayal of his country appeared motivated by greed rather than ideology.
In 1985, Walker agreed to plead guilty as part of a deal with prosecutors to obtain a lighter sentence for his son.
Former Navy Seaman Michael L. Walker served 15 years in prison and was released in 2000.
The brother, retired Navy lieutenant commander Arthur Walker, died at the Butner hospital in July.
The fourth member of the spy ring, Ex-Navy Chief Petty Officer Jerry A. Whitworth was convicted in 1986 and later sentenced to a total of 365 years. A database of federal inmates shows that Whitworth, now 75, is incarcerated at the Federal Penitentiary in Atwater, California.
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