A U.S. Navy intelligence officer came with a proposal to tap an underwater communications cable connecting Soviet Pacific Fleet naval bases around the Sea of Okhotsk.

USS Halibut was once more sent into action for Operation Ivy Bells, as the cable-tapping mission was known. Divers from the sub successfully tapped the underwater cable, an extremely difficult task.

U.S. divers periodically returned to the cable to replace the recorder — until 1981, when the operation was compromised and the Soviets recovered the device.

U.S. submarines have likely conducted many similar missions in the decades since, and those operations have only gained importance in an era of renewed competition with capable adversaries — namely Russia and China.

Beijing has built military bases on manmade islands in the South China Sea, attempting to solidify its widely rejected territorial claims in what is one of the world’s most important trade routes.

The U.S. and its and allies would want to monitor Chinese moves through a number of methods — including underwater surveillance — and provide that intelligence to their policymakers.