More than four centuries after an English merchant vessel struck ground off the Welsh coast, modern researchers have successfully figured out the secret combination of a recovered padlock and unlatched the ancient device.

Peering Inside Without Damage

Specialists uncovered the code, spelling "ANCE," by utilizing high-resolution micro-CT scanning to examine the lock's inner workings safely. This cutting-edge method provided a clear look at the device's internal components and individual rotating brass rings.

“We could see the shapes of the letters on the outside of the rings in the CT scans, as they were impressed into the brass,” David Williams, a research associate at Cardiff University’s School of Engineering, said in an interview. “By identifying the internal notches and matching their positions to the letters on each ring, we were able to determine the correct four-letter combination.”

Whether the word ANCE holds any deeper significance remains an open question. Nonetheless, the discovery paints a vivid picture of the cargo carried aboard the Ann Francis, which met a tragic fate on December 28, 1583, while heading back to Norfolk from Spain. A ferocious storm forced the Elizabethan ship off course, driving it onto Margam Beach near Port Talbot and claiming the lives of 14 sailors.

Historians believe the lock once secured a wooden chest that likely held perishable valuables, such as textiles and confidential documents, which failed to survive the elements.

Treasures From the Deep

Surviving artifacts from the disaster are currently featured in Tides of Treasure, an exhibition at the National Waterfront Museum in Swansea, Wales, marking the public debut of these relics. The collection includes historic gold coins minted during the reign of Spain's Ferdinand and Isabella, alongside a boatswain’s whistle.

Between 1996 and 2017, metal detectorist Peter Hughes unearthed the bulk of the maritime hoard—comprising roughly 870 silver and gold coins, utensils, and equipment—after storms eroded layers of sand on Margam Beach. Amidst the scattered Spanish currency, he discovered the intact lock.

“When I moved the ring dials of the combination they turned with ease after over 400 years beneath the sands and I was left in disbelief,” Hughes said in a statement.

The Science of Scanning

While moving the dials manually was straightforward, unlocking the secret code presented a major hurdle. This prompted a collaboration with Cardiff University’s Musculoskeletal Biomechanics Research Facility, a lab that typically investigates human biomechanics but frequently applies its advanced equipment to analyze animal remains and fossils for archaeological initiatives.

Amgueddfa Cymru, the charitable organization overseeing seven museums across Wales, partnered with the facility team to solve the puzzle.

“In principle, the combination could have been found through trial and error,” university researcher Williams explained. “However, with four rings and six letters on each, there were 1,296 possible combinations, and this assumes you knew exactly where the letters needed to align. Repeatedly manipulating such a delicate historical object could also have risked damaging it.”

Micro-CT technology mirrors standard medical computed tomography scanners, employing revolving X-ray beams and computer algorithms to generate multi-slice cross-sectional views. This allows medical professionals to evaluate injuries and diseases without invasive procedures. Similarly, researchers frequently lean on these non-invasive imaging techniques to analyze ancient artifacts, such as Egyptian mummies.

Scanning dense metals like brass presents unique obstacles because they absorb X-ray energy far differently than biological tissues like bone. Initially, Williams harbored doubts regarding whether the university equipment could penetrate the artifact's secrets.

“I was amazed that we’d actually cracked it,” Williams concluded, “and it was particularly satisfying to hear from the museum team later that evening that the combination had worked and they’d managed to open the lock.”