When John was transferred to Norfolk Virginia, he left Barbara and his family behind to look after the bar. In his new assignment, he served as watch officer in the radio room of the Atlantic Fleet headquarters. In his position, he obtained information on every U.S. submarine in the Atlantic Ocean. Despondent over monetary issues as well as his crumbling marriage, John decided to seek money out for the classified information he was privy to.

In 1967 John stole a key list, a document with codes used to encrypt and decipher classified messages. He took a copy of it and marched into the Soviet embassy in Washington, D.C. He explained to a KGB officer that he was interested in turning over military secrets in return for monthly payments from the Soviets. After looking over the document, the KGB officer agreed. Ignoring instructions from his Soviet handlers, Walker began spending money freely, raising the suspicions of his wife. She pried open a metal lock box in John's office in which she found photographic materials as well as maps and instructions for dead drops. She confronted John and he admitted that he was a spy. Barbara accompanied him to one of his dead drops (later claiming that she wanted to show support for him and their marriage).

John passed on information related to nuclear submarine classifications to the Soviet until he was transferred to San Diego, California to teach radio operations. Worried about losing access to vital information, he looked to develop another source. He found this source in Jerry Whitworth, one of his students. Walker wanted to retire from the Navy so that Barbara, angered over their marriage, would not be able to inform on him. Whitworth, newly assigned to Naval satellite communications school, readily agreed to participate.

Upon returning to Norfolk, John retired from the Navy and divorced Barbara. She and the children moved to Maine while he opened a private detective agency His scheme with Whitworth ran smoothly until Whitworth began asking for more money and threatening to quit. Walker attempted to obtain more money from the Soviet s but also decided to try to find more resources. He began with his children, approaching Margaret and Cynthia, both of whom rejected his advance. Although his daughter Laura entered the U.S. Army.at his urging, she left the service after becoming pregnant. The KGB agreed to give Whitworth a pay raise, allowing his operations with Walker to control.