The Da'at Yichud (Hebrew: דעת ייחוד) is an ancient mystical secret society with some connection to Judaism that has designed and created inventions centuries ahead of contemporary times. Their practices are based on pure reason and are described as a way of understanding God through knowledge and natural law rather than, according to Set Roth, "supernatural bupkis". Their creations never had a purpose beyond the act of creation and were nothing more than a method of communing with God. As such, they were never intended to be used, no matter how powerful they are.
According to Set Roth, the Da'at Yichud is older than the modern religions, and is thus likely several millennia old. The Da'at Yichud have presumably always believed in a monotheistic belief system whereby technological and scientific progress helps them get closer to their god. Since the Da'at Yichud is this ancient, it is possible that their technological creations have inspired later variations of Abrahamic belief systems (modern Judaism, Christianity, Islam) and the supernatural elements of those religions, which the Da'at Yichud do not believe in. Because the Da'at Yichud speak Hebrew and was popular among the later Jewish population, it is also likely the organization arose in ancient Mesopotamia, possibly some time prior to 2000 B.C.E. something that is further supported by claims by in-game characters that they were influenced by the ancient Sumerian civilization from this region. At some point, their organization evidently operated as far away as North America long before later Europeans as remains of their technology have been found also there. Despite the Jewish associations with the Da'at Yichud, the organization is technically open to any gifted individual, regardless of their background or prior beliefs.
The Da'at Yichud had hundreds of vaults containing their knowledge and inventions scattered around the world, and each vault has a gatekeeper. However, the Nazis, led by Deathshead, found one of their vaults, killed the gatekeeper, and stole their secrets. The super war machines the Nazis produced with the knowledge were perversions and mockeries of the religious society's work, and allowed the Nazis to win World War II.
Set Roth is one of the known members of the Da'at Yichud who survived the Nazis' purge. He joined the Kreisau Circle against the Nazi regime, helping them by finding one of the Da'at Yichud safe-keeps in the Atlantic Ocean. The extent of the artifacts the Kreisau Circle obtained from that vault is unknown, as there were not many to be seen in it.
During the events of The Old Blood, it is heavily implied that the Da'at Yichud had existed during the era of King Otto and the document he found to create The Monstrosity was based on an ancient Da'at Yichud genetic technology.
During the events of The New Colossus, an investigation and examination conducted by Nazis scientists on captured Da'at Yichud technology showed that these craftworks are so remarkable that it looks like magic at first glance, but is, in fact, 100% scientific upon close examination.
One extraordinary fact about the Da'at Yichud is the invention of sophisticated technologies such as anti-gravity engines, directed-energy weapons, and mind-control devices during pre-industrial eras. A prime example is the vault in New Mexico which contains research on anti-gravity technology built before European colonization.
Communion with God is thought by the Da'at Yichud to take place through dreams, and enhanced by hallucinogenic drugs.
Despite a good amount of their technology falling into the hands of the Nazis, the Da'at Yichud's advanced technologies still can resist the Nazis. Many Nazi reports show that a lot of Nazi scientists, engineers, and technicians perished from handling excavated Da'at Yichud artifacts improperly. One officer bled out from touching an artifact; a technician was disintegrated after dropping a Da'at Yichud artifact on the ground, and the person stood next to him got a third degree burn. This made the Nazis conduct a manhunt for Set Roth, the only known living member of the Da'at Yichud, and force him to work for them in an effort to prevent these incidents from happening again.
However, Set was broken out of Camp Belica by B.J. Blazkowicz and the Kreisau Circle, and has formed a strategic alliance between what remains of Da'at Yichud and currently active resistance forces, acting as their main scientist, engineer, and archaeologist.
The Nazis began to suffer setbacks by 1960, as Set Roth gave the Kreisau Circle and the American Resistance access to untouched safe-keeps such as the one beneath the Atlantic, leading to the destruction of Deathshead's Compound and the stalling of Nazi scientific advancements.
- Cairo (Helga made discoveries there, when she was first discovered by Deathshead)
- Istanbul (possibly, Helga discovered documents that lead to Deathshead's technology there)
- Atlantic Ocean Trench (where the upgrade for the Laserkraftwerk can be found)
- Roswell, New Mexico (Set Roth mentioned that there was a cache near the infamous location, which was given to the US Government before the Nazis won the war.)
- Paris, France (Where William J. Blazkowicz can be found studying the God Key. Located in a cave under Siegturm.)
- Da'at Yichud roughly translates to "knowledge of the unification" in Hebrew.
- In-game, Set Roth pronounces Da'at as "Da'as", in line with the Yiddish pronunciation of Hebrew words.
- Ironically, Jews are deemed by the Third Reich as enemies of the state and are being exterminated, but the Nazis actually achieved world domination by using Jewish knowledge and technologies.
- This runs contrary to the historical Third Reich's tendencies to scoff upon "Jewish science", most notably the works of Albert Einstein. However, it's perfectly in-line with the historical Third Reich's secret nuclear weapons program, which depended upon Albert Einstein's theories.
- The real-world timeline may therefore be interpreted as what happened when the Nazis never discovered these technologies.
- The Da'at Yichud seem to pay a lot of attention to aesthetic detail, with most of their facilities and technology being seemingly gold-plated and richly decorated. The Nazis, on the other hand, are very practically orientated, and all their technology is clear from decoration. However, this 'aesthetic' may also have practical purposes as well, modular, improved shields, or even stealth technology. Or better at withstanding the pressure of remote locations such as the bottom of the sea, or deep underground. The Nazi knockoffs are good, but true Da'at Yichud technology tends to be much stronger.
- The safe-keep used by Deathshead was described by Set Roth as "small" and "tentative".
- Much of the Da'at Yichud's technology, including the contents of the Da'at Yichud Safe, strongly resembles that of the Dwemer (Dwarves) from Bethesda Softworks' franchise, The Elder Scrolls.
- Da'at Yichud as a story element appears to be a science-fictional re-imagining of the historic Judaism-derived transcendental tradition of Kabbalah. While the historical practices of Kabbalah seek an understanding of the divine and the infinite through study and esoteric disciplines, Set Roth describes Da'at Yichud as seeking communion with God through advanced scientific and technological study.
- It is revealed that the mysterious Roman dodecahedrons are actually Da'at Yichud artifacts, indicated that several ancient but advanced Roman tech like the Roman concrete, or flexible glass are Da'at Yichud inventions.
- Seth Roth claims in his diary in The New Colossus that the Da'at Yichud is actually far older than modern religions, even Judaism, indicating that it is likely not actually a Jewish creation but simply something that became popular among Jewish citizens, or that modern Judaism arose later amongst the members of the Da'at Yichud. It is possible that Da'at Yichud in the Wolfenstein universe represents a stem belief system from which Abrahamic religions like Judaism, Christianity, and Islam would eventually emerge, possibly interpreting such technological wonders as the supernatural elements in their respective mythologies.
- According to resistance fighter Maya Gillam, the Da'at Yichud are believed to have been influenced by the ancient Sumerian civilisation, as the Nazis use Sumerian tablets to help decrypt very old Da'at Yichud language. This further supports the theory that the Da'at Yichud likely arose around the dawn of human civilisation around the Mesopotamian region.