World War II
During World War II, the Templars, who were the ones behind the War, were panicking as their puppets escaped their control and at the scale of the destructions. The Inner Sanctum then decided to help the Americans develop an Atomic Bomb to quickly end the conflict. John Von Neumann proposed a much less destructive solution, to create a time machine to stop Hitler before he came to power, but the Sanctum rejected his idea. Behind the back of his superiors, Von Neumann nevertheless contacted Colonel Boris Pash and the Assassin Brotherhood for help, proposing a temporary alliance. 
In 1943, after Pash forced the hand of the Templars, by putting an end to the Riese Project of Gero Kramer, the Inner Sanctum finally granted permission to Von Neumann to work with the Brotherhood on the Rainbow Project. By studying the Apple of Eden which Pash had taken from Kramer, Von Neumann discovered the "Zero Time", an equation which in conjuction with Die Glocke, a generator of wormholes created by Nikola Tesla, and the Apple could theoretically allow time travel. After Von Neumann convinced Tesla that they could make it work, the Templar/Assassin team settled on the USS Eldridge, an US Navy warship. However, despite multiple attempts, the Templar and his team failed to make Die Glocke work as they intended it to.
On October 28, as they powered Die Glocke again, Von Neumann informed Pash that it was their last attempt to prove the viabilty of the Rainbow Project to the Inner Sanctum or they would force him to join the Manhattan Project. However, as Pash went to fetch for Tesla so he could operate the device, he discovered that the disgruntled Assassin Eddie Gorm had infiltrated on board and murdered the scientist. Ironically, Gorm killed Tesla because he believed that the old man was developping the Atomic Bomb, but only caused the Rainbow Project to be cancelled and the departure of Von Neumann for the Manhattan Project, which ultimately gave the Atomic Bomb to the United State. After the Rainbow Project was shelved, Von Neumann somehow kept the Apple of Eden.
In 1957, Pash, escorted by fellow Assassin Alekseï Gavrani, visited Von Neumann at the Walter Reed Army Medical Center in Washington, D.C., as the Templar was dying fom a cancer likely caused by X-ray over-exposure during his research on the Atomic Bomb. After Gavrani took care the two soldiers guarding Von Neumann, Pash ordered the Assassin to make sure nobody disturbed him while he was talking to Von Neumann alone. When Pash came back from behind the curtains, he was putting Von Neumann's Apple of Eden into his coat and told Gravani that his old friend had just died, "probably" from his cancer. He then told Gavrani to leave discretly while he was dealing with the military.