Is parking a Humvee with the hood open while in the field a thing?

We always did it with our 1/4 ton jeeps and other tactical vehicles. The windshield is the largest reflective surface on your vehicle, and reflections can reveal your position to your enemies.

Yes for the tactical vehicles and 2 1/2 ton trucks. 5 ton and Hemmit's we had camp bags strapped to the roof for deployment. Every Unit on Bragg did it in the 90s.

80's & 90's. We carried Camo bags on the roof and would open the bag flap and drop it over the windshield. if we had an actual "got to go now" moment, we had them rigged with 550 cord so we could flop them back over the top.

I was in the old 9th Infantry Division (Motorized) at Ft. Lewis in the 80's when HMMWV's were still fairly new, and it was SOP to raise the hood when parked in a tactical environment. Later units I was in we had rolled up burlap that we would unroll to cover the windshield.

Yes we did this.

Nope, as part of the "30 Minute Drill" putting the camo nets up was in the SOP!

yes it was standing operating procedure while in the field.

I was in the artillery. If we could put our rubber sleeping matt in the window it was faster to move out. If not, we opened our hoods as well.

We did not open our hoods. If you have to move out quickly then you had to secure your hood before you could move wasting time. We had sandbags for the headlights and canvas for the windshields.

Never heard of it and we never practiced it.