A trickle of strangers were all that were left alive
Tanks in Roppongi! At a special event celebrating the imminent opening of Sengoku Jieitai 1549!
OK, they weren't really tanks. They were "giant armored vehicles" (巨大装甲車).
I also found this handy page about the older Sengoku Jieitai book/movie*, which has the same basic setup (SDF travels back in time, fights Nobunaga) but different characters.
* Released in English as G.I. Samurai, a fact I never get tired of.
Will:
What's the tag line for G. I. Samurai? "A Real American Bushido" would be a good one.