Once upon a time, there was History B. In that world, humans were slaves of the anunnakku, who were something approximating gods. Human language and perception were redesigned by them to make subliminal control not only possible but commonplace. The šedu, servants of the anunnakku, looked human, but had the ability to control anyone at any time.
Something went wrong. Maybe a šedu went rogue; maybe the anunnakku control started to break down. In any case, somehow, a massive reality quake was triggered, and history itself was rewritten.
We live in History A. The ontoclysm happened in 535 AD; any history before that is a scrim of false events constructed out of the human collective subconscious, some of it echoes of the true anunnakku empire. (Some artefacts surface, from time to time; these pragmaclasts, or reality shards, bestow great power on the wielder.)
Not all of the anunnakku, or even all of the šedu, are gone. Sometimes they, or their creatures, break free of the sub-reality they now inhabit. If enough of them succeed, if enough humans start to believe in them again, history might flip back into the global mind-controlled empire... and that's if we're lucky.
Starting in 1888, human researchers began to be aware of this situation. British archaeologists found items that didn't match the rest of the historical record; terrible creatures were unearthed, and (just barely) killed. Gradually they started to dig into the little information they had, with the development of propaganda tools an effective spin-off.
During the Second World War, the British met the American group that had been doing much the same things - working with propaganda tools and group dynamics. The combination became Project SANDMAN.
The Project has always stayed in the background; part of the problem with fighting anunnakku is that any random human trait - such as the way organisations work - may turn out to be a path to invasion and influence.
For forty years, the šedu have turned over operations in our reality to their lieutenants, the aquatic kulullû. That led to belief in ancient astronauts, UFOs, and general mysticism. Large parts of the Project were infiltrated and turned.
The kulullû's Y2K memetic campaign was a failure, but the šedu returned. It's not clear what they're now doing, but they've been active at the old sites in in Mesopotamia - Iraq - as well as Libya and Afghanistan.
The fundamental mission of Project SANDMAN is to contain and defeat the Anunnakku. This mission depends on humanity at large never realizing the nature of the threat: either global panic or global worship would provide the Anunnakku with the psychic energy to awaken and return the world to their ordered, tyrannical history. Thus Sandman missions must always be covert and clandestine; even friendlies with top-secret clearances and vital knowledge must be approached under cover or false flag if at all possible. Witnesses to unambiguous irruptor activity must be killed, blanked, discredited, or recruited.
Sandmen have carte blanche to carry out this mission. If they fail, there won't be a review board.
Secondary missions include: