I don't know, but I do remember reading that one characteristic issue of them is that the errors compound over time. If you're say, dropping a GPS-guided bomb,

I don't know, but I do remember reading that one characteristic issue of them is that the errors compound over time. If you're say, dropping a GPS-guided bomb, and the signal is jammed, then they'll fall back to INS for the rest of the way. The distance between signal loss and impact is pretty short, so there isn't much time for errors to compound. If you're navigating say, a submarine however, the longer you go without a real fix, the more unreliable that INS estimate is going to be, especially if maneuvers have been undertaken. In other words I guess, "it depends". =)