Pact of Kulgotha
The Pact of Kulgotha is an agreement between the Adeptus Mechanicus and the Dark Angels Chapter. Forged circa M33, the pact appears to allow the Mechanicus to call on the Dark Angels for aid but the circumstances and specifics are unknown.
Some members of the Dark Angels, including Danatheum, believe that the Chapter has done enough over the years to free them from the Pact. However, this does not appear to have stopped the Mechanicus from invoking it, and the Dark Angels have continued to hold themselves to their oath.