I think 3D printing has many potential military uses and these two stories demonstrate the potential.
Researchers at the University of Sheffield have created a low cost disposable unmanned aircraft making extensive use of 3D printing
3D printing unmanned aircraft is not new but it is an interesting story anyway.
And this one, looking at contour crafting, or 3D printing buildings. Although the details are a bit vague, the potential for military building is obvious
This from me looks at the potential for printing or 3D contour crafting in military engineering