Citadel by Robert Doherty
At the start of the Cold War, the greatest threat to America wasn't the Russians and the looming Communist threat. Rather, it was an elite organization bent on world domination, a group so powerful only nuclear weapons could safeguard against them. The CIA knew what these men were capable of, and in a last ditch attempt to protect America against them, they built two high–security arsenals deep within the earth––one declassified in the Nevada desert, and one heavily under wraps in Antarctica. For over 50 years, no one spoke of The Citadel, the fortress deep under the ice in Antarctica that held the most powerful weapon known to man––until the Organization returned, hellbent on destruction.
Captain Jim Vaughn is a government agent known for performing missions no one else wants. So when an old colleague approaches him with an assignment, he can't refuse––even if the mission has been set in motion by a dead man's letter, found in Antarctica and dated 1949. The Citadel has been cracked, and the only man who can safeguard it is Vaughn. Nothing short of the fate of mankind rests on his shoulders.