Sound of the Sky (So Ra No Wo To) was the hit Military x Music anime from early 2010. It was produced by A-1 Pictures and Aniplex and directed by Mamoru Kanbe of Elfen Lied and Cardcaptor Sakura
The anime revolves around a young girl named Kanata Sorami who is inspired to join the military after witnessing a rendition of “Amazing Grace” by a mysterious trumpeter of the Army. Becoming a bugler, she is assigned to the 1121st Platoon and together they try to enjoy life in a post-apocalyptic world regressed by war.
Sound of the Sky is finally getting a Blu-ray version after seven years. You can already get a pre-order on RightStuf, before the June 6, 2017 release.