It’s interesting to go back to ‘first principles’ on airspace management, and in particular the declaration of restricted areas. Regulations 6 and 7 of the
Airspace Regulations 2007 relevantly say:
6 Designation of prohibited, restricted or danger areas
(1) CASA may, in writing, make a declaration designating an area of Australian territory to be a prohibited area, a restricted area or a danger area.
(2) CASA must not declare an area to be a prohibited area unless, in the opinion of CASA, it is necessary for reasons of military necessity to prohibit the flight of aircraft over the area.
(3) CASA must not declare an area to be a restricted area unless, in the opinion of CASA, it is necessary to restrict the flight of aircraft over the area to aircraft flown in accordance with specified conditions in the interests of any of the following:
(a) public safety, including the safety of aircraft in flight;
(b) the protection of the environment;
(c) security.
(4) CASA must not declare an area to be a danger area unless, in the opinion of CASA, there exists within or over the area an activity that is a potential danger to aircraft flying over the area.
…
7 Publication of a designation
(1) CASA must cause a declaration designating an area to be a prohibited area, a restricted area or a danger area to be published:
(a) if the declaration is to have effect for a period of 3 months or longer—in the AIP; or
(b) in any other case—in a NOTAM.
(2) Publication of a declaration of a restricted area must set out the conditions in accordance with which the flight of aircraft over the area is permitted.
…
There are a couple of very important things to note out of that:
First, restricted airspace is about - or is supposed to be about - what is happening in the area of Australian territory
underneath the airspace. For example, mine blasting could put at risk the safety of aircraft flying over the mine. For example, the security of some classified installation on the ground might be put at risk if aircraft could fly over and ‘spy’ on the installation.
Contrast danger areas, which are about activities
within the danger area (or in the area of Australian territory underneath the danger area) that are a potential danger to aircraft. Look closely and compare the words in regs 6(3) and 6(4): “over” versus “within or over”. For example, intense flying training is something happening
within airspace, which is why they are generally declared danger areas.
Short point: Military aircraft flying around in a chunk of airspace is not, of itself, sufficient for the valid declaration of that chunk of airspace to be “restricted”. Restricted airspace is about the risks caused by or to stuff on the ground/water
underneath the airspace (provided it’s in Australian territory).
Secondly, and in any event, restricted airspace is usable on satisfaction of conditions. Those conditions of use
must be published along with the declaration of the restricted area (reg 7(2).
Short point: There is no such thing as an ‘active’ restricted area that cannot be used, no matter the circumstances. (That's a 'prohibited' area.) All restricted airspace is useable, subject to conditions, which conditions must be published.
At least that’s the theory.
Alas, mere trivialities like the law rarely get in the way of airspace management in Australia. Out of many, many examples, does anyone recall the conditions of use of the restricted area recently declared, by NOTAM, around Shepparton? I don’t recall them being published in the NOTAM.
(And for the sake of completeness: The ADF has no separate power to designate airspace.)