I hate those bucket-loads of IMHO redundant tags that get poured on if you allow that.
Science Fiction.Military answers all the questions:
It is Fiction
It is Military Fiction
It is Fiction - Science Fiction (Doh!)
Bucket loads of tags is a holdover from the days of paper-board cards in drawers (remember them?) when you needed a separate CARD for each (major) category (I don't ever remember any Library filing by the granularity I see in many of the current tags

)