DAGR stands for Defense Advanced GPS Receiver. When grown-ups go on special missions for the military, they use a GPS device to know where they are on a map. DAGR is like a super-good GPS device that helps the grown-ups be very accurate in knowing where they are, even if it's dark or if there are tall buildings that usually block the GPS signal.
It's like your toy car that goes wherever you make it go with your remote control, but it can go far and even in places that are hard to see. DAGR helps the grown-ups know where they are and go where they need to go without getting lost or going the wrong way. It's a very useful tool to help keep them safe and complete their mission successfully.