Earlier quoted context omitted.
How in-house does it need to be? The actual physical facilities aren't being shut down; they're just under new ownership and management. And Nippon Steel is located in Japan, which is such a dependable ally of the US that I'm politely trying not to use the phrase "vassal state." Also in the US, we've got Steel Dynamics (producing 75% as much as US Steel), Cleveland-Cliffs (approximately tied with US Steel), and Nucor…
US Steel was a major contributor of steel for the WWII military machine. Honest question: if WW3 were to start, would we be able to appropriate Nippon-owned USS factories for wartime use?
The law that would specifically come into play here is called the Defense Production Act, and it’s complicated.
Here’s a great overview:
https://www.cfr.org/in-brief/what-defense-production-act
For more specifics, I would look at this overview which is excellent:
https://www.businessdefense.gov/ibr/mceip/dpai/dpat3/docs/DP...
In wartime, seizing capacity from an ally is… problematic. That’s my concern. What is technically possible isn’t necessarily diplomatically viable, and there are quite a few layers of laws here.