You may/probably all ready know of this site but -- http://www.militaryfactory.com -- is a great site for all things military. You can find United States military signals for all the branches (Army, Navy, Coast Guard, Air Force) and you can even look up military vehicles from across the decades.
well, i just found the site and i suggest you check it out, it can be very helpful if you need inspiration. Also like i said before it has everything on it.
Sorry if someone already beat me too this.