Get into a WAR then try and import the Steel you need.....
You nail the most serious problem. It was the fact that we were able to produce more than double the combined steel production of the axis powers that gave us the insurmountable edge in World War II.
In an age of ICBMs, satellites, and a permanent human presence in orbit, the idea that mass-producing military hardware like tanks and ships will have any role in a major armed conflict is silly.
The only traditional military hardware that will matter will be the stuff that exists on the day the shooting starts. This isn't the 1940s. The entire surface fleets of nations could be sunk within hours.