When you reach "Lies of the Past: Checkpoint 4", you will ascend in an elevator. Exiting the elevator, you will see a replica of the Moon's surface, a model of the U.S. space suit, and a shuttle the United States used to reach the Moon. This is in reference to the Moon Landing Conspiracy, claiming that the U.S. never actually reached the Moon, and faked the landing to beat the Russians in the space race. Additionally, go to a building behind the crane operations and scan a top secret file. Go back to the secrets in the campaign menu and play Doctor Cray's diary to hear him say something similar to "Man certainly has been to the moon but the horrors of the alien life form that reside there have never been revealed to the public." This refers to the theory that there is alien life form on the moon and that the government chose to hide it from the public.
Submitted by kallum moses