Drinking On Duty: Averted inasmuch as neither the Imperial Navy nor the Imperial Legions, nor indeed any other part of the Imperial Military Service is dry, even on duty.  Drinking enough to render yourself unfit for duty, on the other hand, and the punishment for same, is played very straight indeed.

On the third hand, between the biotech upgrades you start out with and the ones which you acquire mid-way through boot camp for your shiny new military-basic body, you would have to drink truly heroic quantities of booze – enough that you’re unlikely to be able to have it with you on post, unless your duty station is engineering and you’re slurping the reactor coolant directly – in order to render yourself unfit anyway.  (This does mean that you can’t drink to forget the horrors of war, but since you can visit a memory redactor for that, it’s probably not so bad a trade-off.)