[95th Rifleman]

Necessity is the mother of invention, it's a maxim of war as old as war itself.

In a full blown shooting war the peacetime methods of procurement and development go out of the window. Field mods become approved for factory builds and beurocratic redtape is thrown out of the window for quick deployment of required equipment.

I'd suggest a study of WW2 allied and german vehicles as a good starting point for this. In peacetime you can afford to scrap oboslete desighns, in war you convert them to something more useful (the Germans where masters of this paticular art, turning old tanks into effective gun platforms).

Rather than new systems, we'd see older ones being retasked. Take the M60, this would make a great base for a whole series of variants from up-armoured APCs to gun platforms and SAM/AAA platforms.

For instance you could take off the turret on an M60 and run a 120mm from the M1A1's and turn the M60 into an assault gun that is low and can be deployed in a defensive role with the same firepower as an M1 but in a cheaper (and more expendable) package that saves the valuable M1's for more aggressive deployments. This is exactly what the Germans did with their older panzers.

Take the old M113s and put various turrets onto them for expanded roles. When you cut away the peacetime crap and beurocratic nonesense you get some rapid and imaginative batlefield variants that do the job they need to do.