The Da'at Yichud is an ancient Jewish secret society 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 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. That was until one of their vaults were discovered and looted by Nazi forces who reverse engineered them to make their super war machines that were perversions and mockeries of the religous society's work.
The Da'at Yichud had hundreds of safe-keeps containing their knowledge and inventions scattered around the world, which kept them from falling into the wrong hands. However, the Nazis led by Deathshead found one of their safe-keeps, stole their secrets and used them to win World War II. Even after the war, Nazi research into Da'at Yichud technology are continued in labs such as the London Nautica to create and/or reverse-engineered new weapons such as the LaserKraftWerk.
Set Roth is one of the known members of the Da'at Yichud who survived the Nazis' purge and helped the Kreisau Circle against the Nazi regime, and finding one of the safe-keeps in the Atlantic Ocean. It is not known the extent of the artifacts the Kreisau Circle obtained from that vault, as there are not many to be seen in it.
During the event of The Old Blood, it is heavily implied that Da'at Yichud has existed during the era of King Otto and the document he found to create The Monstrosity was based on ancient Da'at Yichud genetic technology.
- Cairo (Helga made discoveries there, when she was first discovered by Deathshead)
- Istanbul (possibly, Helga discovered documents that lead to Deathshead's technology there)
- Deep Sea Trench
- Da'at Yichud roughly translates to "secluded knowledge", or "seclusion knowing" in Hebrew.
- Ironically, Jews are deemed by Third Reich as enemy of the state and are being exterminated, but the Nazi 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.
- The Da'at Yichud seem to pay very large attention to aestethic detail, with most of their facilities and technology being seemingly gold-plated and overly decorated. The Nazis on the other side, are very practically orientated and all their technology is clear from decoration.