Summary: I am in the mlitary and the use of this GPS was solely in a field environment. I orginally purchased this product when I went to the National Training Center at Fort Irwin, CA. As a tank commander, I used it only when I was dismounted. There is no external antenna attachment so it was obviously useless inside the tank, even with the hatch open. A buddy of mine had a magellan in a Bradley and his worked and my Garmin did not. The next test was in Iraq.