Drawing intricate designs in 3D is an art form unto itself and many people would prefer to buy or download file rather than trying to lead how to design it from scratch.  Thankfully there are a few resources online that you can turn to in order to locate 3D files of military emblems, logos and designs.
www.cncmilitaryemblems.com - This site has many military emblems that are already designed in 3D can can be easily 3D Printed or CNC carved. The pricing is very reasonable when you consider how much time it would take to learn how to do this.
www.designandmake.com - This website has a lot of 3D designs that you can buy. There are some military ones that you can assemble into various models for specific designs.  You can buy files individually or as a set.
www.thingiverse.com - Thingiverse has been around for a while and is basically a huge index of just about anything you can imagine.  You will find some military designs and emblems on there by doing some simple searches.  The best part about this site is that everything is free to download.  Keep in mind that you do not have the right to sell the designs you download, but you can use them for personal needs.  If you are working on a commercial project you should reach out to the person who designed the file and arrange to obtain rights to resell.
If you know of any other websites, please email info@stepcraft.us so we can add them to this list