The official answer for Spain would be the one provided by Danielillo. Nevertheless, this is not what happens in day to day life. In informal communication, most officers tend to use tú when addressing subordinates. But there are exceptions. For instance, in the Navy it is customary for officers to use usted and even Don when addressing high ranking NCOs.
I once met a Navy Commander who always addressed his assigned Warrant officer as Don José. He explained me that this use was based on the roles in a ship (they were both actually working at the High Command, on land) and many Navy people liked keeping this tradition.
Age also comes into consideration. Usually, young officers don't feel confortable addressing veteran subordinates as tú and may resort to usted.
In summary: subordinates almost always address their superiors as the ordnance says, but superiors tend to use tú when addressing subordinates, with some exceptions.