Use it? The US invented it. The US has historically funded it as part of their human rights initiatives. Like I said:

Also many of the sponsored projects help people circumvent authoritarian government overreach, which is something that until recently has been considered "good" for the US. The more freely information can flow the harder it is for authoritarian regimes to exert control.

Given the nature of the Tor network, it's likely any "official" use within the US government would probably involve things like communicating with people working undercover / informants, etc., and not be something broadly discussed.