A new exhibit in Jerusalem has revealed for the first time an unusual variation on one the most famous encryption devices in history — a Hebrew text version of the World War II-era German Enigma machine.

The Jerusalem Bloomfield Science Museum this week opened its CAPTCHA exhibit to mark 70 years since the development of the electronic computer. Among the various artifacts on display is the curious example of an enigma machine.

The device was one of several acquired by the Israel Defense Forces in the years after the establishment of the state in 1948, Yedioth Ahronoth reported on Thursday. The machines were tinkered with to adapt the keys to accommodate the 22 letters used in the Hebrew alphabet and then pressed into service to keep the new state’s military secrets under wraps.

However, apparently unbeknownst to Israel’s military, the seemingly secure Enigma machine codes had already been cracked in what was one of the most closely guarded secrets of WWII.

The Enigma machine was invented at the end of World War I and used by the German military from the 1930s onward to encrypt messages. With trillions of possible combinations, its codes were considered impregnable. However, following on earlier breakthroughs by Polish intelligence services, in 1939 a British team led by Alan Turing at Bletchley Hall finally managed to break the Enigma machine codes, giving the allies an inestimable advantage over the Nazis.

The success was one of the most closely guarded secrets of the war and afterwards, as Britain encouraged former colonies that had gained their independence to use the enigma machines for their own military secrets.

Turing’s accomplishment was only made public in the 1970s, by which time the machines were obsolete.

The science museum exhibit celebrates the various stages in the development of computers and gets its unusual name from the acronym “Completely Automated Public Turing test to tell Computers and Humans Apart,” which is a variety of methods utilized in computing to verify that a user is, in fact, human. Internet users will be familiar with common CAPTCHA tests on websites that ask for coded numbers to be typed as confirmation before setting up some accounts.