Divers searching for discarded fishing nets in the Baltic Sea have discovered a rare Enigma encryption machine used by the Nazis in World War II.

As AFP reports, a team found the Enigma machine last month in Germany’s Gelting Bay, which is about 90 miles (150 km) north of Hamburg. The device, famously used by Nazis to encrypt messages during the Second World War, was uncovered by a group not normally associated with marine archaeology: the World Wildlife Federation (WWF). German divers working on behalf of the group were searching for abandoned fishing nets, also known as “ghost nets,” when they accidentally stumbled upon the historic relic.

“What a find,” said Florian Huber, an archaeologist and research diver, at his Facebook page. “I will not forget this day. Once in a lifetime.”

A diver inspecting the historic artifact.Image: Florian Huber

Huber normally conducts archaeological dives, but on this day he happened to be assisting the WWF with its environmental protection program. Talk about serendipity and some seriously good karma. After the discovery, one of Huber’s colleagues “swam up and said: there’s a net there with an old typewriter in it,” he told the DPA news agency. On closer inspection, the group realized they had found something of historical significance.

On Friday, the group handed the Enigma machine over to a German museum for restoration. Ulf Ickerodt, head of the archaeological office in the Schleswig-Holstein region, told DPA it’ll be a delicate process, and the desalination of the machine alone could take upwards of an entire year. The rare Enigma machine will eventually go on display at a museum.

The Nazis used Enigma machines to encrypt and decrypt radio messages transmitted during the war. Unbeknownst to the Germans, however, British intelligence at Bletchley Park, with the help of mathematician Alan Turing, cracked the system in 1941. The 2014 film The Imitation Game dramatizes this historical episode, but the real story, and how events unfolded after, is considerably messier. Regardless, the cracking of the Enigma machine had a material impact on the course of the war.

As to how this particular machine ended up at the bottom of the Baltic Sea, it’s tough to say. Naval historian Jann Witt from the German Naval Association told DPA that it was likely tossed overboard from a German warship during the late stages of the war, as this particular unit has three rotors, not four (rotors were used to display different letters of the alphabet). This machine probably didn’t originate from a scuttled submarine (as Huber suspects), because German U-boats were equipped with the more complex four-rotor versions, according to Witt.

Thousands of Enigma machines were produced by the Germans in the 1930s and 1940s, but very few are still around today. Approximately 50 Enigma machines of various types are currently on display at museums around the world, with more existing in private collections. In 2015, a rare Enigma M4 (four-rotor) machine sold at auction for a record $365,000.