That requirement wasn't in the original statement.
Nor would the guys in Iraq give a ratsass where the armor came from once the bullits start flying.
If they can make it, make them make it, and if they don't want to, Nationalize them and do it at gunpoint.
"Because we only have ONE American factory that makes steel for our armor, that's why. IF we want more American armor, we need to manufacture more American Steel."
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Steel comes in different grades, so even if the soldiers didn't care where it comes from at first, they would care after it failed.