Whistles & Bugle Calls

I think the way to look at this card is that you are using it to order a group of units that are connected to each other by being adjacent. This group of units in some scenarios may actually go from one side of the board to the other.
The important thing to remember about ORDERing a unit is that you are not required to move it, nor are you required to battle with it. So using this card creates an opportunity for a units movement and battle but not a necessity.

Is this a single order that all adjacent units have to obay?