Is Girls & Panzer: Shoukai Shimasu! hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV Special · 2012 · 2 episodes · PG-13 - Teens 13 or older
CGDCT, Military, School
Specials aired between episodes five and six and episodes ten and eleven, both recapitulation episodes.
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