I did this for a UK-based defence company back in 2002. I used a single top mounted lens that was like a fisheye, but more so (that is, more than a hemisphere of view) with a helmet-mounted inertial box to track the direction of view the driver was looking in. The entire more-than-a-hemisphere of captured imagery was post-processed to match what the driver would see were the tank transparent in the direction he was looking. Lag was good enough that you could drive around a car park with it. Not quite so swish as this, true, but cost about the same back then as this does now (a few thousand all in for the single prototype - would have been much less in production). "See-through armour", as the phrase we used as the time had it. We had plans to fill in blind spots on request with additional cameras, and a recording was kept so that at a later time, someone could play back the tank's journey but look wherever they liked (we hypothesised sticking it on vehicles in hot places so that after a vehicle patrol anyone interest could have a good look at everything, or play back any incidents).<p>The UK MOD (or rather, one of their gatekeepers at the time) weren't interested so we binned it. I expect they were only interested in solutions costing millions of pounds. :)