The game is based on the "Cthulhu Mythos" created by horror writer H.P. Lovecraft, in particular on the novella "The Shadow Over Innsmouth", but is not a direct adaptation of any of Lovecraft's stories.
Among the collectible documents in the game, there is one revealing that Charles Reed, during the war, fought in the same platoon as Solid Snake, the protagonist of the "Metal Gear Solid" franchise.