During the Cold War, the United States wanted to learn more about Soviet submarine and missile technology, specifically ICBM test and nuclear first strike capability.
In October of 1971, the United States sent the purpose-modified submarine USS Halibut deep into Soviet territory in the Sea of Okhotsk. Its mission was to find the undersea telephone cable that connected the Soviet submarine base at Petropavlovsk on the peninsula of Kamchatka to the Soviet Pacific Fleet at its mainland headquarters at Vladivostok. They were to eavesdrop on the wire with an instrument that measured electromagnetic emanations. The mission was successful. What they heard was easily understandable Russian conversations with no encryption. The following year, Halibut installed a permanent tap on the line to record the conversations, with a plan to return in about a month to retrieve the records. Eventually more taps were installed on Soviet lines in other parts of the world—the more advanced instruments were nuclear powered and could store a year's worth of data. The recording device was built by AT&T's Bell Laboratories. Other submarines were utilized for this role, including USS Parche. All in all, the intelligence gathered from these exercises helped end the Cold War, as it gave the United States a window directly into the Soviet mind (Sontag and Drew 1998)" from Blind Man's Bluff: The Untold Story of American Submarine Espionage.
Although created as a cover story, this mission was actually carried out with great success: US naval divers recovered all of the SS-N-12 supersonic AShM debris, with the largest debris no greater than 6 inches, and a total of more than 2 million pieces. The debris was taken back to the US and the US Naval Laboratory reconstructed the AShM based on these pieces, and at least one sample was also reverse engineered. It was discovered that SS-N-12 AShM was guided by radar only, and the IR guidance previously thought did not exist. From the samples built, countermeasures were successfully developed and deployed.
It is important to note that no documents were passed from Ronald Pelton to the Soviets because Pelton had an extremely strong memory. Ronald Pelton reportedly received only a total of $35,000 from the KGB for the intelligence he provided from 1980 to 1983, and for the intelligence on the Operation Ivy Bells, the KGB gave him $5,000. Surprisingly, the Soviets did not take any action despite the fact that Pelton had provided the details of these operations.
In July 1985, Vitaly Yurchenko, a KGB colonel who was the initial contact of Ronald Pelton in Washington D.C. defected to the US, and provided the information that eventually led to Pelton's arrest — it was only then that the Soviets acted. To this day, it remains unclear why it took the Soviets so long to act. The recording device captured by the Soviets was on public display in a museum in Moscow.