Nana Toshi Monogatari: Hokkyokukai Sensen

Sci-fi that's set in the future but the military which is the central theme aesthetically feels like army of the past. Predominantly adult cast with similar character designs. Both are also based on works by the same writer. 

Nana Toshi's plot is about a large naval battle between two armies using sci-fi versions of WW2 ships. Characters and plot are very similar to Legends of the Galactic Heroes: Two genius strategists at Commodore rank in each army fight a battle of wits. Like in LotGH, one of them is a blonde achiever, the other a dark haired rebel. The novel the OVA is based on is by the same author, Yoshiki Tanaka. Beside the occasional girl friend and corrupt politician, literally all characters are soldiers, and 95% of the screen time is about strategy meetings or actual battle action. The use of maps to explain strategy is also strikingly similar. read more