[dannyw]

That's what it was. The NSA was reverse proxying Google.

The legit explanation (given the domain name) is probably they wanted to use reCAPTCHA, but block all non-NSA hosts with a firewall or something.

This is not great, because the NSA expanded its attack surface to all of google.com.

The more conspiracy explanation is that this is actually a phishing page set up, and due to a misconfiguration it's exposed under captcha.nsa.gov, but Occam's Razor should apply here.

[littlestymaar]

I think you meant “Hanlon's razor”[1].

[1]: https://en.m.wikipedia.org/wiki/Hanlon%27s_razor

[mirimir]

As far as I can tell, it's what you'd see hitting https://www.google.com.br/ from Brasil, but in English.