In terms of widescreen, this game is an oddball. First of all, it's important to note that this is not a 3D game in any way. The earth in this game is not a 3D globe, it is a 2D vector rectangle where the top sides end and the left and right sides are seamlessly "connected" without forming a curve. If you can, imagine a conveyor belt where the outside of the belt has a map of the earth on it, and the underside has a length of zero.
Since the map is 100% 2D vectors, you can actually take zooming into consideration here, because in a 2D environment, moving the camera backwards is the same thing as zooming out (it's a different thing in 3D environments). Anyway, if you zoom out all the way, it is anamorphic.
4:3
16:10
16:9
But if you zoom in all the way, it's vert -.
4:3
16:10
16:9
And perhaps another way to look at the game; zooming to an intermediate level, to the point where you get ideal vertical coverage for any given situation. In this case, it is hor + (look at the right edge of each picture)
4:3
16:10, zoomed out a bit
16:9, zoomed out a bit more
In my opinion, the third example is the best representation of Defcon's widescreen handling. The second example is not a good one at all, because in any situation where widescreen is vert - and vert - is not desired, you can just zoom out a little bit to make it hor + (again, this doesn't work well in 3D games). So I think this game should be classified as "Hor +."
I think it's unlikely that anyone will disagree with me here, but just in case someone does, I'm going to wait at least 20 hours before grading so that anyone who wants to debate this has the opportunity to. If there's no controversy in 20 hours, I'll grade this and add it to the MGL.
