Combat Field Fortifications used in the Ardennes Offensive
Field fortifications come in many variants of size and function. Both are vital and essential to the success of combat units on both sides. To simplify the explanations, the theory and practices are put to use by all armies involved in the conflict. Too many people state only that, the woods are full of "holes dug by GIs". Even though the statement is true, it isn't that simple. There are functions, of each hole (Shelter) manned, names of shelter/fortification types, and the combination of location, types, function, and placement lay the foundation of the objectives to accomplish, whether it is offensive or defensive.
Here in the picture to the left is a great example of a machinegun position that has been taken by US forces, the diagram on the right from FM 21-100 shown in regulation how an MG position would be built.