@Kuraiaku That's a different thing that is written & read differently in Japanese but is written exactly the same when romanized.
Army otaku: 軍オタ (軍: army, read: "goon")
Gundam otaku: ガンオタ/ガノタ (ガン: "Gun", the first two letter of the Japanese word for Gundam (ガンダム), read: "gun")
Interestingly...