I imagine something like they dropped some of that sun hot plasma on civilians or they broke out area-denial munitions. If some bright spark could turn the gamma gun into a bomb it would be....effective.
Given the prevalence of high energy plasma warheads in everything air-dropped munitions to grenades they should have at least plasma shells. Probably also high explosive because it is cheap and gets the job done for soft targets.
Considering Bloodflies and Bloatflies exist operations to clear out the concentrations of insects in South America are going to include plasma flamers and rotary cannons.
I always found it weird that in the later Fallouts it has been up to 200 years post-exchange and people live in scrap houses. I think despite the devastating conflict the humble sawmill and ability to use nails would stay in fashion.
On the one hand ending the last remnants of those who dropped the bomb in a mushroom cloud was rather poetic, but it did make all your proof of global genocide expanding plasma.
Considering your Fallout 4 protag will by mid-game have turned hundreds of living thinking people into corpses, it would be weird if he wasn't a killing machine. My gun is driving railroad spikes into the livers of anyone who looks at me funny, I am not a model of conventional morality.
The original internet came from very similar beginnings as well, in the coming decades just like OTL technology and economic pressures should push a wider network into public use. As for the NCR winning, despite the US taking some body blows the sheer amount of industrial, manpower, and...
This makes me wonder just how warped internet culture is going to be once they get around to inventing that. That and high performance computers that don't weigh a few tons and need enough power to light up an apartment complex.
So with some new hardware in the pipe and the reserves coming up, can the under-performing US military rally to leverage their material superiority. Love the new tank design bringing together all the cutting edge technology we saw Pre-War into production.
I like the tasteful cut before that man has his head pounded midway through his rib cage. PA in close combat is going to result in what would look like a set of horrific industrial accidents.