Imagine being inside a submarine during World War II.

The boat is dark, cramped, and sweating with tension. Men whisper at their stations. The captain studies a target through the periscope. Somewhere above, enemy escorts are hunting. Every sound matters. Every second matters.

Then comes the order.

Fire.

A torpedo leaves the tube, rushing toward an enemy ship. For a few moments, everyone waits for the distant explosion.

But something is wrong.

Instead of running straight, the torpedo begins to curve. Its guidance fails. Its steering system betrays its purpose. The weapon turns in a wide, deadly arc through the water—not toward the enemy, but back toward the submarine that launched it.

This was the horror of a circular run: one of the most feared torpedo malfunctions of the Second World War.

What Was a Circular-Run Torpedo?

A circular run happened when a torpedo malfunctioned and began turning back toward its firing submarine. Torpedoes relied on gyroscopes, depth controls, steering mechanisms, and later acoustic homing systems. If something failed, the weapon could stop behaving like a straight-running projectile and become a lethal boomerang.

For submariners, this was uniquely terrifying because there was almost no time to react. A torpedo moving at high speed underwater could complete its deadly curve in seconds or minutes. The launching submarine might be slow, deep, damaged, or already trying to evade enemy escorts.

The nightmare was simple:

You fired the weapon.
Now the weapon was hunting you.

The Confirmed Horror: USS Tang

The most famous confirmed example was USS Tang, one of the most successful American submarines of World War II.

On her final patrol in October 1944, Tang attacked Japanese shipping near the Taiwan Strait. At about 2:30 a.m. on 25 October, she fired her last torpedo, a Mark 18 electric torpedo. It broached, curved left, and entered a circular run. Tang tried to maneuver clear, but roughly 20 seconds after launch, the torpedo struck near the aft torpedo room.  

The explosion sank the submarine in about 180 feet of water. Out of 87 men aboard, only 9 survived. Some escaped from the sunken submarine using Momsen lungs, one of the rare real combat uses of that emergency escape device.  

Key Takeaway: Circular runs were not just theoretical. USS Tang proved that a submarine’s deadliest enemy could become its own torpedo.

Why Did Torpedoes Do This?

World War II torpedoes were advanced but imperfect machines. They had to travel underwater, maintain depth, follow a course, arm safely, and detonate at the right moment. That required complex mechanical and electrical systems operating in a harsh environment.

A circular run could happen because of:

• Gyroscope failure
• Steering malfunction
• Incorrect settings
• Mechanical damage during launch
• Depth-control problems
• Acoustic homing confusion
• Design flaws in new torpedo technology

German U-boats also used advanced torpedo types, including pattern-running and acoustic torpedoes. U-boat technical references describe German torpedoes as 53.3 cm weapons with large warheads and note systems such as FAT and LUT, which intentionally made torpedoes run complex search patterns after missing a target.  

Those systems were meant to make torpedoes more dangerous to convoys. But any weapon that could turn, search, or home also carried a frightening risk: under the wrong conditions, it might find the wrong target.

German U-Boats and the Self-Torpedo Fear

Some German U-boat losses have long been suspected of involving circular-running torpedoes. The challenge is that submarine losses were often mysterious. A U-boat might vanish without survivors, without a wreck, and without a clear Allied attack report. In those cases, historians have to compare radio messages, convoy records, wreck damage, and postwar documents.

U-972 is one example. It disappeared in the North Atlantic after its last radio message in December 1943. Some accounts report speculation that it may have been sunk by one of its own circling T5 torpedoes, though other explanations point toward Allied action and the wreck has not been found.

U-869 is another debated case. Divers who found the wreck off New Jersey believed it might have been hit by its own torpedo. But official evaluations rejected that theory and credited U.S. destroyer escorts with the sinking.

That uncertainty is part of what makes the topic so haunting. In many cases, the ocean kept the final answer.

Why a Circular Run Was So Terrifying

A submarine crew could understand enemy danger. Depth charges, aircraft, destroyers, mines, and patrol ships were expected threats. They were part of the job.

But your own torpedo turning back was different.

It was betrayal by machinery.

A submarine firing a torpedo was usually trying to remain hidden. The boat might be near a convoy, surrounded by escorts, or operating at night in dangerous waters. If the torpedo malfunctioned, the crew had only moments to detect the problem and maneuver away.

Inside the submarine, men might hear the torpedo’s motor or receive a warning from the sound operator. Then came the desperate command to turn, dive, accelerate, or reverse. But underwater, submarines were not agile enough to dodge easily.

The terror was not only death.

It was the knowledge that the fatal shot came from your own tube.

The Cruel Irony of Submarine Warfare

Submarine warfare was built on stealth and patience. A submarine stalked its target, calculated firing angles, and released a weapon meant to kill from hiding. But a circular run reversed that relationship.

The hunter became the hunted.

The torpedo became the predator.

The firing solution became a death sentence.

That is why circular-run stories still grip people. They compress all the fears of modern warfare into one image: a machine built to obey turning against the people who trusted it.

Conclusion

The circular-run torpedo was one of World War II’s most nightmarish weapon failures.

It was not superstition. It was real. USS Tang’s sinking remains the clearest and most tragic proof: one of America’s greatest submarines destroyed by her own final torpedo. For German U-boats, several losses have been suspected as possible circular-run incidents, though many remain debated because evidence is incomplete.

In the silent world beneath the sea, submariners already lived with crushing pressure, darkness, enemy sonar, and explosive death from above.

But few fears were worse than this:

You fire at the enemy.

You wait for the explosion.

And then, through the headphones, comes the sound no one wants to hear.

Your own torpedo is coming back.

Frequently Asked Questions

What is a circular-run torpedo?

A circular-run torpedo is a torpedo that malfunctions and turns back toward the vessel that fired it, potentially striking its own submarine or ship.

Did submarines really sink themselves with their own torpedoes?

Yes. The clearest WWII example is USS Tang, which was sunk by her own circular-running Mark 18 torpedo in October 1944.  

Were German U-boats sunk by their own torpedoes?

Some German U-boat losses have been suspected as possible self-torpedo cases, including U-972 and U-869, but not all are confirmed. In some cases, official records favor Allied attacks instead.  

Why would a torpedo turn back?

A torpedo could turn back because of gyroscope failure, steering malfunction, acoustic homing confusion, incorrect settings, or other mechanical problems.

How fast could this happen?

In USS Tang’s case, the torpedo struck the submarine about 20 seconds after being fired.  

Why were circular runs so feared?

Because a submarine had little time and limited maneuverability underwater. A malfunctioning torpedo could become impossible to avoid.