In 1969, the Soviet navy shocked the U.S. and NATO militaries with a new and incredibly capable submarine—one that could swim faster and dive deeper than could anything else under the sea.

But the seven high-tech Alfa-class submarines—each able to reach 45 knots of speed and 2,400 feet of depth—actually were inferior where it really mattered. Their speed and depth-resistance came at the cost of noisy internal machinery that made them easy to detect … and destroy.

“The Alfa was a huge step forward in submarine design,” retired Royal Navy sub commander Doug Littlejohns told naval expert Iain Ballantyne. But considering all of the sub’s limitations, “what is the point?” Littlejohns added.

Ballantyne describes the Alfa’s revolutionary features in his books Undersea Warriors and Hunter Killers—starting with the boat’s streamlined all-titanium hull, which one Soviet officer compared to an expensive work of art or a spaceship. An Alfa was relatively small at 240 feet long and carried a crew of just three dozen.

The CIA was able to determine the new boat’s abilities fairly quickly by studying scrap metal from the Soviet Sudomekh shipyard that somehow wound up at a recycler in Pennsylvania, and by recruiting “stroller” spies along the Neva River waterfront, where the Sudomekh yard was located and where the prototype Alfa was taking shape in 1969.

According to Ballantyne in Undersea Warriors, some U.S. intelligence officials were skeptical at first that the Alfa really was meant to be an operational attack submarine, one that Soviets would build in meaningful numbers.

“According to a recently declassified CIA case study, the skeptics in U.S. naval intelligence circles maintained ‘the shaping and welding of heavy titanium hull sections, especially in the generally “dirty” shipyard atmosphere, was impractical, if not impossible.”

It wasn’t until the early 1970s that the CIA fully understood the truth. The Alfa was an operational boat. The Soviets were building multiple copies in addition to the prototype. And the Alfas were faster and deeper-diving than were any other submarines in the world. “One of the most revolutionary submarines ever constructed,” is how Ballantyne describe the class in Undersea Warriors.

Soviet leadership “lavished attention and money on the Alfas -- so expensive but highly capable they were dubbed ‘golden fish,’” Ballantyne wrote in Undersea Warriors. “They were the elite of Russia’s submarine force. No wonder, for the Alfas appeared to offer technological parity and even superiority over the West.”

But the new boats had serious weaknesses.

The Alfas featured powerful new 155-megawatt nuclear reactors providing 40,000 horsepower, making them like underwater race cars. “The amazing acceleration rate enabled the Alfa to go from six to 42 knots in just 120 seconds,” Ballantyne wrote in Hunter Killers, “but the use of liquid metal for reactor coolant was extremely radical—and very dangerous.”

Moreover, the high speed “created a lot of noise,” Ballantyne pointed out in Hunter Killers. In combat with a slower, less-deep-diving American, French or British submarine, an Alfa could speed away from enemy torpedoes and dive so deep that the pressure crushed the munitions.

But the Alfa never stood a chance of hitting back against its attacker. “As soon as the Alfa came back up to actually try and fight NATO boats, it would be nailed due to its noise signature,” Ballantyne asserted in Hunter Killers.

By contrast, American, French and British subs were more “balanced,” according to Ballantyne in Hunter Killers. They combined good speed, depth performance and—most importantly—quiet machinery that helped them to sneak and survive in wartime.

The Soviets retired six Alfas by 1990 and the seventh in 1996. The successor Victor III and Akula boats were, like their NATO rivals, balanced—and thus far more fearsome in combat, even if they were slower and lower-diving than the revolutionary Alfas were. The Akula was the first Soviet boat to match NATO vessels in quietness when it entered service in the early 1980s.

David Axe serves as Defense Editor of the National Interest. He is the author of the graphic novels  War Fix, War Is Boring and Machete Squad.