Natsufuku no Shoujo-tachi

In 1945, the second and third-year students of a Hiroshima girls' school are taken away to work in war factories. The remaining 220 girls of the first year try to make the best of their new-found status as the only teenagers in an almost deserted town, even amid the deprivations of wartime. On the 7th of August, an American bomber changes their lives forever. Broadcast on the 43rd anniversary of Hiroshima in memory of "the girls who lost their lives to the atom bomb."

(Source: Anime Encyclopedia)