The US Government's Secret Grand Central Station Basement Explained

Grand Central is well known both as one of the symbols of New York City as well as its status as the world's largest train terminal. According to Gothamist, it spans 49 acres underneath the ground of Manhattan and sees more than 700,000 people pass through its halls each day. However, there is one detail about Grand Central that is less well known: its deep underground basement. In fact, this secret area is so far underground that a ten-story building could fit beneath the floor of the main concourse and still not reach the basement. The area was so guarded that the government did not acknowledge its existence until the 1980s. Moreover, at several points during its history, any trespassers would be shot on sight.

The deep underground basement was originally created for a practical purpose. The New York Central's train system originally ran on steam power, and as a result, tunnels were often plagued with poor visibility from all the water vapor. The issue came to a head in 1902, when a collision under Park Avenue killed 15 people and injured several more, per PBS. Six years later, steam engines were banned throughout the city and New York Central "set out to find an alternative," according to Untapped Cities

This alternative was the switch to electric rails, which required enough space to fit more than 850 tons of electrical equipment.

The Nazis attempted to infiltrate this secret basement in World War II

Since the basement houses the electricity that powers much of New York City and the surrounding area's rail infrastructure, it became a target of German spies during the outbreak of World War II. 

According to Untapped Cities, Nazi spies entered New York Harbor on U-boats in the hope that they could enter the basement and attack the ten rotary converters that transferred alternating current into direct current. Their method was to use sand to cause the converters to short on electricity and delay the movement of troops across the Northeast.

Fortunately, the U.S. Coast Guard spotted the Germans coming ashore, and from there, the FBI tracked their movements and arrested the men before they could undertake any attack.

Though most of the rotary converters have been replaced by more modern equipment that still powers the rails today, a few of them remain in the basement as a symbol of their importance in New York's history.