Divers trying to remove old fishing nets from the Baltic sea have accidentally stumbled on a Nazi code-making machine.

The Enigma machine, as it's called, looks a bit like a typewriter. In fact, the diver who found the device on the ocean floor initially thought that's what the artifact was, according to AFP. But the diving team, on assignment for the conservation group World Wide Fund for Nature (WWF), quickly realized that they had something much stranger.

During World War II, Enigma machines were used to encode German military messages, in hopes of preventing Allied powers from learning about troop movements and other plans. The devices consisted of a keyboard and a series of rotors that did the encoding. The rotors substituted different letters for the ones typed in; different Enigma machines used between three and eight rotors, which moved independently after each keystroke so that the same initial letter typed into the machine would appear as multiple different letters in the final code.

While searching for abandoned fishing nets, German divers discovered this Enigma machine in the Baltic Sea. (Image credit: Uli Kunz/WWF)To decode the message at the other end, an operator just needed to know the starting position of the rotors and the routers between them. Once the encoded message was entered into an Enigma machine with the right configuration, the machine would spit out the original text.

Cracking the Enigma code was an enormous part of the Allied war effort. Polish mathematicians Marian Rejewski, Henryk Zygalski and Jerzy Różycki made the first attempts in 1939 and were able to recreate a mock-up of the Enigma machine, explain its basic functioning and decode many messages. They then handed this information over to British intelligence, according to the BBC, because the Germans were changing the codes daily, making it more difficult for the Polish team to decipher their messages.

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British mathematician Alan Turing was crucial to the effort to decode the German Navy's Enigma messages, which were more complex, according to the Imperial War Museums. Cracking those codes was crucial for saving Allied ships from German U-boats, the submarines that sank more than 5,000 ships during World War I and more than 2,700 during World War II.

The Enigma machine found by the WWF diving crew was at the bottom of the Bay of Gelting in northeast Germany. It had three rotors, making it the type used on warships, not U-boats. That suggests that the machine may have been tossed overboard in the final days of World War II, in an attempt to keep the technology out of enemy hands, historian Jann Witt of the German Naval Association told the DPA news agency.

The divers turned the machine over to the archaeology museum of the German state of Schleswig-Holstein, where archaeologists are restoring it. That project should take about a year, according to Ulf Ickerodt, head of the state archaeological office. The Enigma machine will then go on display at the museum.

Originally published on Live Science.