The following isn’t fiction. Prepare for a tale of underwater politics, espionage, and treachery.

It’s the early 1970s. American and Soviet leaders debate how and if they can limit their nuke arsenal.

Despite pretenses, tensions remain high. Each side is vying for the upper hand, that scrap of intelligence that will bolster their diplomatic position.

The CIA, NSA, and Navy think they’ve found it. They believe that they’ve found a potential treasure load of information: A Soviet unencrypted communication line.

Resting on the bottom of the Sea of Okhotsk, which divides the Kamchatka Peninsula and Siberia, the American intelligence and military think that the Soviet Navy has a cable linking a major Pacific Fleet naval base with its mainland headquarters.

They’re right.

The White House receives a daring proposal. If the cable can be tapped, Capt. James Bradley Jr., Naval Intelligence Undersea Warfare chief, and a WWII submariner, argues, America might gain vital intelligence on its adversary and thus gain the upper hand in the nuclear talks; potentially even know if the Russians are about to push the red button of world destruction. The White House agrees.

Operation Ivy Bells is a go.

At first, the technical difficulties seem insurmountable. Technology for such a mission simply doesn’t exist. Divers can’t survive underwater long enough to finish the job, and the U.S. toolkit doesn’t have the kind of advanced wiretap required.

Worry not, says the Navy. We’ll replace nitrogen with helium for the divers, and invent a device suited for the delicate process of tapping.

Similar to how Delta Force and SEAL Team Six pioneer gadgets and procedures that then trickle down to the rest of the military, Operation Ivy Bells revolutionized underwater technology.

October 1971.

USS Halibut (SSGN-587), a special operations-capable sub, leaves port. Within its hulk, lies a mysterious 20ft long device, which will be wrapped around the cable, thus limiting the chances of compromise, and three-feet tape recorder. The recorder (which was probably history’s largest telephone tap) can be detached in the event the Soviets raise the cable for maintenance.

The mission is so classified that few onboard know about it. The rest of the crew believe that they’ll be recovering debris from a sunk Soviet anti-ship cruise missile, the P-500 Bazalt (a variation of which is still in use by the Russian navy).

USS Halibut reaches the Sea of Okhotsk undetected and sets to work. Her divers find the cable at 400ft.  But the water temperature is insanely low, and they retreat into the sub. A solution comes in the form of a cord that will pump warm water in their dive suits.  It works.  The divers then finish the bugging.

Like a whisper in the dark, USS Halibut vanishes. On her way home, she retrieves the P-500 debris (eventually, the U.S. Navy managed to reconstruct the missile and built countermeasures for its ships).

Immediately, a wave of intelligence reaches Washington. Success.

For the next decade, U.S. subs would make the dangerous biannual journey to the Sea of Okhotsk to retrieve and replace the tapping apparatus. U.S. intelligence gathered valuable intelligence on the Soviets’ nuclear intentions and their navy.

The crew of USS Halibut received a Presidential Unit Citation for their daring.

And if it weren’t for the treachery of Ronald Pelton, an NSA employee with financial troubles who in 1980 sold the secret to the Soviets, Operation Ivy Bells would’ve continued.

Why didn’t the Soviets encrypt the line? They were, after all, famous for their ciphers and codes. Although no answer exists, it was probably because they didn’t believe someone could pull off an Ivy Bells.

It’s like the patrol commander who after a long day pitches camp on top of a hill and leaves the cliff unguarded, confident that the terrain is a sufficient defense. But then the night comes and with it the enemy.

Some aspects of Operation Ivy Bells remain classified.

This article was originally published in February 2020. It has been edited for republication.