medium to large defence companies tend to have in house board fabs. I worked in one.

yes, what was the utilization like?

20-40% capacity. Reserve available. Turnaround same day on a board (2 layer). Next day 4 layer. Two days exotic (rogers etc). Pick, place, soldered 2 days or delivered to lab immediately after panel cut.

If they had a fast production run in they could extend to 24 hours operation and triple base capacity.

They did a fair bit of TH though which was manually stuffed and wave soldered which could slow stuff down considerably.

Very interesting, I'm wondering if that low-utilization rate justifies the capex of building a line.

Low utilisation would be a good thing as they would value availability to the line very highly.

Yes and no, I could imagine a system where they have on demand capacity with a company like us and pay for that service.

It's mostly for security reasons. Both supply chain and secrecy.