Consider the following hypothetical:
The President learns that China is going to arm Russia with weapons in its war in Ukraine. The United States, unlike Russia, is not on a war footing. Its economy is not mobilized and its citizens are not being mobilized to work production in the defense sector. Ukraine's munitions requirements and usage already outpace US munitions production capacity.
So to respond, the President considers proposing the following the Congress: (only presenting the relevant portions of this 'plan' or thought experiment related to the question)
I want to use the US National Guard & possibly US Army Corps of Engineers to build 10-15 new munitions productions facilities across the US quickly (utilizing tens of thousands of National Guard personnel or more), and then staff said production facilities with National Guardsmen until the contractor obtains new hire replacements (with government incentives).
Would this be legal, to use National Guard personnel (and possibly Army) for construction and even manufacturing personnel on a temporary basis, particularly when it can be linked to US national security or "supporting the functions" of the United States military?