Board Thread:Theories/@comment-30413782-20161105051814/@comment-32031502-20170517102811

Actually you cannot see their military structure using modern army equivalent. Take Levi for example, his "rank" is  兵士長 Heishichō. 兵士 means soldier/soldiers (single & plural) and  長 means leader here thus he is a leader of soldiers, not an actual rank. People in the manga shorten it to  兵長 Heichō which is also Lance Corporal in WW2 Imperial Japanese Army, thus the weird translation between Captain and Lance Corporal. Levi has no rank! Erwin Smith "appropriated" Levi into the Survey Corp (see OVAs), thus he is outside military rank. Hange technically outrank Levi but he answers only to Erwin Smith.

Mikasa is indeed named after WW2 battleship but not because of nationalistic pride but a rabbit foot's belief among mangaka artist that naming female characters after WW2 battleships brings luck and the manga will sell well.