None of the full size helis, military or civilian, can hover inverted. The biggest limiting factor is probably the main shaft and its support structure. To make a full size main shaft strong enough to take the helis full weight inverted, it would have to be very large. That much extra weight would take away from its primary mission, just to add an ability that most, if not all users would have no use for. To see what I'm talking about, see how much weight you can hang from a drinking straw, then try to support the same weight on top of the same straw.