Very true about defendability. Look at all the trouble the Germans had with partisans and Allied commandos sabotaging the railways in the occupied countries during World War II. In addition to large numbers of troops needed to hunt partisans in general, large numbers were tied down guarding the railroads in particular.
Don’t look for US armored trains at any time in the near future, for the very simple reason that it’s far easier for an enemy to blow out the tracks and bridges than tangle with rail-borne armor. Then the mighty armored train wouldn’t be able to go very far and would, in fact, be quite vulnerable.
If the military-industrial-congressional complex EVER listed to troops in the field, it would surprise me. By now it should be quite clear that a lot of people get very rich off of government contracts for military equipment, supplies and services. Providing troops (i.e., throw-away people) with what they need comes in last in priorities.
As for “public spirit and patriotism” (or is it “conquest and plunder” of oil-rich lands these days?) I’m not sure what the commercial railroads exactly will be expected to do. They can’t shanghai their employees into going to foreign lands on behalf of the government. If the government wants something, it’ll need to pay for it. The railroads aren’t in the charity business.