The United States Bullion Depository, often known as Fort Knox, is a fortified vault building located adjacent to Fort Knox, Kentucky, used to store a large portion of United States official gold reserves and occasionally other precious items belonging or entrusted to the federal government.
The United States Bullion Depository holds 4,577 metric tons (5046 tons) of gold bullion (147.2 million oz. troy). This is roughly 2.5% of all the gold ever refined throughout human history. Even so, the depository is second in the United States to the Federal Reserve Bank of New York's underground vault in Manhattan, which holds 7,000 metric tons (7716 tons) of gold bullion (225.1 million oz. troy), some of it in trust for foreign nations, central banks and official international organizations.
The fortress-like structure lies the gold vault lined with granite walls and protected by a blast-proof door weighing 22 tons. No single person is entrusted with the entire combination to the vault. Several members of the Depository staff must dial separate combinations known only to them. Beyond the main vault door, smaller compartments provide further protection. The facility is ringed with fences and is guarded by the United States Mint Police. The Depository premises are within the site of Fort Knox, a United States Army post, allowing the Army to provide additional protection. The Depository is protected by layers of physical security, alarms, video cameras, armed guards, and the Army units based at Fort Knox, including Apache helicopter gunships of 8/229 Aviation based at Godman Army Airfield, the 16th Cavalry Regiment, the 19th Engineer Battalion, formerly training battalions of the United States Army Armor School, and the 3rd Brigade Combat Team of the 1st Infantry Division, totaling 30,000 soldiers, with associated tanks, armored personnel carriers, attack helicopters, and artillery.
There is an escape tunnel from the lower level of the vault to be used by someone accidentally locked in. Since the opening of the depository, the Federal government has disclosed very little information about the security systems and technologies used. What is generally known about the security systems at the Gold Depository mostly dates from the late 1930s. For example, the small turret-like structures at the corners of the building are firing positions for guards with Thompson submachine guns, the standard longarm of the Mint Police when the Depository was built. It is rumored that everything from minefields, to ground-sweeping radars, to body capacitance wires, to automated machine guns triggered by interrupting laser beams are emplaced to guard the building and its approaches. It is rumored that, like the French national bank in Paris, the vaults can be filled with water. The Federal government will neither confirm nor deny the rumors. Employees are sworn to secrecy and cannot divulge information about the vault's security.
For security reasons, no visitors are allowed inside the depository grounds. This policy has been enforced ever since the vault opened and the only exception was an inspection by members of the United States Congress and the news media on September 23, 1974 led by then Director of the United States Mint Mary Brooks.