The Flag
Because the American flag is a symbol of the whole American nation, it deserves great respect. When they see the flag is being raised, soldiers will stand right away and even salute at times. No knee-droppers here.
Back To The Wall
In the military, when your back is towards the wall, it doesn’t mean that there is nowhere else for you to go. It actually means you’re safe because you don’t need to watch out for threats behind you. You only need to mind what is in front of you. Soldiers have the tendency to opt for a seat that has a wall right behind them even when they are back to civilian life.