There are a lot of WW2 References in this series so far, Ouka is much like the Japanese suicide plane developed during ww2, launched from a bomber. Not only that, the patch on the last page of this manga with the nurse reads "731" a biological warfare unit known to perform disgusting human experiments. The cold northern country was likely the Soviet Union during the battle of Khalkin Gol where they dealt the Japanese a very bloody nose.

All in all there are a lot of references to WW2, though the dates dont match up.