Digging in, a TOAW III "improvement" ?

[Currahee]

It could be several things; it's rare to see a drop that great within one hex, but by no means impossible. Most likely is that something is interdicting the supply, such as a super river or suez canal with no bridge; flooded marsh; and, I think, alpine; and supply is having to come around the "long way", rather than over the river, marsh or mountain, accounting for the drop. Terrain in the hex you actually occupy is also a factor, but wouldn't alone cut it to level 1. Enemy zoc also interdicts supply, altho that effect is canceled if you have a unit actually occupying the hex in question. So, for example, a combination of super river and enemy hexes may be interdicting your supply; it would be at zero, but if there is another, non-interdicted route that is much longer, that could explain the 1.

Feel free to send me a screen shot, but if you are seeing a drop from 50 to 1 in one hex, there are probably one or more of the above terrain features which, along with enemy zoc's, are interdicting supply.

Note also that major fording units, or engineers on a destroyed bridge hex, can cancel the interdiction effect of the super river/ suez canal. Or of course, repairing a bridge.