Fifty-six years ago, a Soviet submarine lurked off Oahu, ready to unleash destruction on Pearl Harbor far greater than that experienced on Dec. 7, 1941.

The diesel electric Zulu-­class B-88 sub likely had a T-5 nuclear-tipped torpedo on board armed with five kilotons or more of explosive firepower.

“If it detonated at the harbor mouth or inside the shipping channel, it would have devastated both Pearl Harbor and Hickam Air (Force) Base, as well as killing hundreds if not thousands of those present,” said Carl Schuster, a retired Navy captain and adjunct professor at Hawaii Pacific University.

The deployment remains an overlooked chapter in the Cuban Missile Crisis of October 1962, which many historians believe is the closest the world has come to nuclear war.

Now a new nuclear arms race is unfolding, renewing worries about the mass destruction and casualties it would bring.

“Ever since the dawn of the nuclear age, the world has gradually developed a consensus that nuclear weapons are so destructive and abhorrent that it would be unacceptable to use them,” wrote Nina Tannenwald in this month’s Foreign Affairs magazine.

But the “norms and institutions of nuclear restraint are unraveling,” said Tannenwald of the Watson Institute for international and public affairs at Brown University. In the face of new strategic competition between the United States, China and Russia, arms-­control agreements are being abandoned.

More than ever before, “humanity risks facing a future in which the nuclear taboo, a hard-won norm that makes the world a safer place, is in retreat,” Tannenwald said.

The Cuban Missile Crisis involved Moscow’s placement of short-, medium- and intermediate-range nuclear missiles on the Caribbean island led by Fidel Castro in a direct threat to the United States. A dangerous cat-and-mouse game between U.S. Navy ships and Russian submarines carrying the same T-5 nuclear-tipped torpedoes evolved over the 13-day period between Oct. 16-28, 1962.

Aiea resident and retired Navy Capt. Jerry Coffee played a key role in the crisis. He was the pilot who uncovered the existence of short-range “Luna” tactical surface-­to-surface nuclear missiles in Cuba on Oct. 25, 1962.

In a blistering run at 460 miles per hour, just 500 feet off the ground, Coffee, flying photo reconnaissance in an RF-8A Crusader, diverted from his flight path a bit to get pictures of a suspicious-looking military camp.

The now 84-year-old Coffee recalled in a phone interview that he was “kind of holding my breath” during the daring runs. The photos revealed the camp had the 2-kiloton Lunas, which would have been deadly for a U.S. land invasion — and a probable instigator of a larger nuclear war.

President John F. Kennedy had announced a blockade of Cuba on Oct. 22. The crisis heightened when three Soviet Foxtrot-class subs were detected nearing Cuba and efforts were made to force them to the surface — with U.S. officials unaware they carried nuclear torpedoes.

U.S. ships dropped grenade-sized practice depth charges, which, to the crew of the Soviet B-59 sub, “felt like you were sitting in a metal barrel, which somebody is constantly blasting with a sledgehammer,” crew member Vadim Orlov later recalled in an interview that was translated from Russian.

Without the ability to surface, take on air and recharge its batteries, temperatures in the sub reached more than 120 degrees. As carbon dioxide levels increased, sailors “were falling like dominoes,” Orlov said.

The ship’s rattled captain, Vitali Savitsky, who could not reach higher-ups, ordered the nuclear torpedo assembled to battle readiness. “We’re going to blast them now! We will die, but we will sink them all! We will not disgrace our Navy!” Orlov remembered the captain saying.

But Savitsky “was able to rein in his wrath,” and after consulting with two other officers, he decided to surface.

Cuban Missile Crisis expert Svetlana Savranskaya wrote that if a Soviet sub captain had used a nuclear torpedo, the U.S. Navy likely would have responded with nuclear depth charges, “thus starting a chain of inadvertent developments which could have led to catastrophic consequence.”

Schuster, the retired Navy captain, said that because the Soviets probably believed their national survival was at stake, “having a submarine positioned to take out the Pacific Fleet and its headquarters as required would be a prudent move.”

“From the Soviet perspective, warning of a fleet sortie would have been vital to preventing or being prepared for a (Navy)-­based nuclear strike,” he said. At that time, aircraft carriers had nuclear weapons.

“Also, taking out Pearl Harbor might prevent a second or third (Navy)-based nuclear strike or (bombers including) B-52s and B-47s staging through Hawaii,” he said.

Instead, detente prevailed, and a deal was struck.

Soviet leader Nikita Khrushchev on Oct. 28 agreed to withdraw the weapons from Cuba, and Kennedy pledged not to invade. In a secret addendum not revealed for 20 years, Kennedy also had agreed to remove Jupiter nuclear missiles from Turkey that threatened Russia.

In a sign the crisis was not yet over, Savranskaya said, the B-88 left the Kamchatka peninsula that same day “with orders to sail to Pearl Harbor and attack that U.S. base if the crisis in Cuba had escalated into a U.S.-Soviet war.” It’s believed that B-88 was never detected off Hawaii.

Orders to return were given, then rescinded, with the B-88 finally returning to Kamchatka in December, she said.

The deployment of the Soviet diesel electric Zulu-­class B-88 sub remains an overlooked chapter in the Cuban Missile Crisis of October 1962, which many historians believe is the closest the world has come to nuclear war.