It's even more subtle than that: Lockheed Martin did use metric in the design department that communicated with NASA, but its manufacturing department used impe

It's even more subtle than that: Lockheed Martin did use metric in the design department that communicated with NASA, but its manufacturing department used imperial units. I had a friend (in Europe) who worked as a mechanic on Apache helicopters in Afghanistan; all of that is in imperial too. He worked as a contractor so had to provide his own tools, but those are all in imperial and essentially useless outside of the US. So he now has an expensive high-quality useless toolset. Switching manufacturing from imperial to metric is the real challenge. Nuts, bolt, things that have to fit exactly: it's all very banal, but there's a lot of it and switching it all over isn't easy or cheap.