Not a veteran, but I worked through a strain in the past.
I strained my high hamstring, and ended up doing Rippetoe's Starr Rehab recommendation. It's a very reasonable, logical approach IMO.
Let it rest until it feels like it is healing, maybe a couple week or so, then start with just the bar and do like 3 sets of 20 squats. Next day, add 10lbs and do 3 sets of 20. Every day, add a little bit of weight and just do some high reps and let it work through the range of motion.
It should hurt a bit, but there is a difference between rehab pain and injury pain.
He's got the full protocol up on his website somewhere.
Only applies if it is a pull/muscle belly injury, which I think you would know as you would have heard/felt a little pop; it would have been a very discrete moment when it went from being OK to not right.
If something is inflammed, like tendinitis due to overuse, the only thing I can recommend is rest. Ibuprofen will help, but only mask it and let you train through it potentially making it worse.
Stretching/mobility will help if it is caused by some sort of moving disfunction. I had a nagging hip flexor thing up that I fixed by stretching and changing my form on squats. Lasted about 3 months, and took some due diligence holding some very nasty stretches until it resolved.
I'd recommend experimenting with some stretches until you find something that is tight or aggravated then work through it.