Scientists Crack a 400-Year-Old Shipwreck Lock — But Its Secret Remains

For more than four centuries, a small brass lock kept its secret beneath the sands of the Welsh coast.

It had survived a violent shipwreck, centuries of burial and the eventual discovery of a treasure hoard. Yet nobody knew the four-letter combination needed to open it.

Now, researchers have finally cracked the code using advanced scanning technology. The answer is ANCE. But while one mystery has been solved, another remains: what did those four letters mean, and what was the lock originally protecting?

A Shipwreck Lost in a Violent Storm in 1583

The lock came from the Ann Francis, an English merchant ship that sank off the coast of Wales on December 28, 1583. The vessel was returning from Spain when a powerful storm blew it off course and drove it onto Margam Beach, near what is now Port Talbot.

The ship was carrying valuable cargo, including money received through international trade.

Historical research by Museum Wales reveals that the ship belonged to Francis Shaxton, a merchant from King's Lynn whose family had also been involved in smuggling.

The Ann Francis had sailed to the Iberian Peninsula with a cargo of wheat. Its return journey was supposed to bring the proceeds of that trade back to England. Instead, the ship was wrecked. Contemporary court records suggest that the disaster quickly became the subject of a dispute over ownership of the wreckage.

Local authorities and landowners argued over who had the right to recover its contents, while accusations of looting complicated the aftermath An inventory from the period mentioned weapons, ship equipment, textiles, coins and three chests whose locks had been broken.

Much of the vessel's remaining cargo eventually disappeared beneath layers of coastal sand. It would take centuries for its story to resurface.

The Treasure Hunter Who Found the Mysterious Lock

Between 1996 and 2017, metal detectorist Peter Hughes spent years recovering objects exposed by changing conditions along Margam Beach.

Storms and dredging had removed layers of sand, revealing traces of the lost sixteenth-century cargo.

The discoveries included hundreds of gold and silver coins, personal belongings, navigational equipment and objects used by the ship's crew.

Among them was a remarkably well-preserved brass combination lock. Unlike a modern padlock that opens with a key, this Elizabethan device used rotating rings engraved with letters. The correct combination would release its locking mechanism.

Despite having spent more than 400 years buried in the sand, the rings could still turn. Its construction fascinated museum specialists, but the combination remained unknown.

The mystery was especially intriguing because the lock was found near Spanish silver coins and coin weights. Researchers suspected it had once secured a small chest containing valuable objects.

However, the chest itself had not survived in a form that could establish exactly what the lock protected.

How Scientists Finally Cracked the Four-Letter Code

The breakthrough came when specialists from Cardiff University and Amgueddfa Cymru – Museum Wales decided to investigate the lock using micro-computed tomography, commonly called micro-CT.

The technique uses X-rays to generate highly detailed three-dimensional images of an object's internal structure. It is frequently used to examine biological specimens, including bones, but it can also reveal hidden mechanisms inside fragile historical artifacts. Researchers needed a way to investigate the lock without forcing it open or damaging its centuries-old components.

Dr David Williams, a researcher at Cardiff University's School of Engineering, examined the internal mechanism through the scans. The images revealed how the notches inside the lock aligned with the letters on its rotating rings. By studying those alignments, Williams identified the correct four-letter sequence.

A-N-C-E.

Museum specialists then tested the combination.

It worked. A mechanical puzzle that had survived since Elizabethan England had finally been solved without damaging the artifact. The achievement also demonstrated how modern scientific equipment can help archaeologists investigate historical objects that would otherwise be too delicate to examine internally.

What Did the Secret Code Actually Mean?

Finding the combination did not explain why the original owner chose those particular letters.

The sequence ANCE does not immediately reveal an obvious English word. It could have held personal significance to its owner, but researchers have not established a historical explanation. And the contents of the chest remain equally uncertain. Because the lock was discovered close to Spanish silver coins, it may have protected money or other valuables. Another possibility is that it secured documents, textiles or personal possessions that have not survived.

The historical records describing chests recovered from the wreck add to the intrigue, but they do not establish the identity of the person who used this particular lock. For now, the researchers can explain precisely how the device opened, but not why its owner selected the combination. That distinction is important.

The code has been discovered. Its meaning has not.

A 400-Year-Old Mystery That Visitors Can See Today

The lock is now part of the Tides of Treasure exhibition at the National Waterfront Museum in Swansea, Wales. It is displayed alongside other artifacts associated with the Ann Francis, including rare gold coins, silver currency and a boatswain's whistle. The exhibition brings together objects that illuminate a world of maritime trade, dangerous voyages and international commerce during the sixteenth century.

For historians, the lock is more than an unusual piece of antique security technology. It is a tangible connection to someone who lived more than 400 years ago and wanted to protect something important.

The discovery also shows how much information can survive inside an apparently ordinary object. A tiny brass lock, lost in a storm in 1583, has become the subject of a modern scientific investigation.

And although researchers now know the four letters that opened it, its final secret remains beyond their reach.

Why did someone aboard the Ann Francis choose ANCE — and what was so valuable that it needed to be locked away?

Those questions may never be answered. But after more than four centuries, the mysterious padlock has finally opened.

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