Classification: UNCLASSIFIED
Caveats: NONE
Brian,
I work for the military and would dearly love to go to a dual-stack everywhere, but as Jim mentioned, that's simply not feasible. Unlike commercial users, we typically must develop our own unique comms networks that support unique military requirements (i.e. extremely constrained bandwidth (we feel lucky to have 16KBPS "pipes"), unpredictable, but inevitable and often lengthy, disconnects from network services, and a need for both host and routing infrastructure to be mobile). In such an environment, operating two routing protocols, as you must with dual-stack becomes quite problematic. In addition, because of the lengthy life cycles of weapon systems (15-20 years), you find yourself working with processors that are overloaded already. Throw a dual-stack requirement on this tactical environment and you break the camels back.
So we are typically looking at replacing the entire tactical comms infrastructure. Given the other constraints on bandwidth, mobility, etc., it becomes very attractive to make the leap from IPv4 directly to IPv6 without a lengthy dual-stack transition period. However, that essentially creates an IPv6-only ISP supporting our weapon systems on the battlefield. Of course, this, in turn, comes with another set of problems, primarily for interoperablity with IPv4-based current systems and allies, but we hope by aggressively migrating the force to IPv6-dominance that these additional problems become manageable.
Vr,
Steve