That’s the AT&T Long Lines Building. It probably did have an NSA surveillance closet, but it wasn’t built without windows for that reason. The story I was told (by older colleagues when I worked at AT&T Labs) was that it was built during a time when riots and street violence were more common, so the fortress appearance was to ensure the city could maintain long-distance connectivity during urban unrest.
I believe there was another similar nexus downtown near the World Trade Center, which was destroyed on 9/11. For at least a couple of weeks we had very limited communications and credit cards were hard to use as a result.
Long lines buildings were not going to take a direct nuclear hit, but were very robust to handle shockwaves and EMP.
I came very close to buying a long lines microwave relay site, and got to tour it a few times. It had a hardened tower, as well as copper grounding that went deep into the ground. Mining the copper would have paid for the site, but alas.
These buildings were built based on the 1950s threat of Soviet bombers attacking the United States. The New York City metro area was protected by air defense missile sites and interceptors. The air defense systems would air burst small nukes in wartime to destroy bomber formations.
Once the threat shifted to ICBMs in the 1970s hardening was moot.
Yup, an underground structure would normally be a better design. But that would quickly get flooded with water in Manhattan in the event of a nuclear blast followed by loss of power.
I believe there was another similar nexus downtown near the World Trade Center, which was destroyed on 9/11. For at least a couple of weeks we had very limited communications and credit cards were hard to use as a result.