[michaelt]

Practically speaking, I agree.

But theoretically speaking, the time when a strong manufacturing industry is needed is if you get into a lengthy WW2 style conflict, where both sides burn through their stockpiles of tanks/shells/missiles/whatever.

Then whoever can deliver tanks to the battlefield fastest has the numerical advantage. In 1942 the allies had retooled their car/locomotive/tractor manufacturing plants to make tanks and they were literally producing 9x as many tanks as the axis powers. Which is obviously a very good thing, militarily.

So there is historical precedent for the idea that a strong domestic car/locomotive/tractor industry being very helpful in wartime.

Of course, the question you've got to ask is: Will we ever see another WW2 style conflict? Because in a nuclear conflict there's no time to retool and manufacturing plants, and in lower-intensity conflicts like Vietnam/Iraq/Afghanistan there was no desire to.