I don&#x27;t know, but I do remember reading that one characteristic issue of them is that the errors compound over time. If you&#x27;re say, dropping a GPS-guided bomb, and the signal is jammed, then they&#x27;ll fall back to INS for the rest of the way. The distance between signal loss and impact is pretty short, so there isn&#x27;t much time for errors to compound.<p>If you&#x27;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.<p>In other words I guess, &quot;it depends&quot;. =)