I support Flash Light!!!
Why?
Team chat is not always a decent way to communicate while in the heat of battle. Have you thought about using a flashlights to communicate? A flashlight could be used to communicate even in the fog.
If a soldier had field manual, it could be informations on how to use Morse Code and what should be carries like maps, campass etc. Yes, you need to know what the lights message means as senders and receiving end. Or else it is just a soldier turning on and off a flashlight.
How about your choice?