Takao
The Bunker Group
There are excellent reasons that a Brigade is the unit of action for Army, and not a Battlegroup.
Enablers: A BG cannot sustain itself past 14 days at the most. Some will be much less than that. Furthermore, while there will be a mix of infantry and armour, a BG is rather one-dimensional. Because of these, the BG needs to be reinforced with combat support and logistic elements. When you are talking about artillery, Army aviation, RAAF, RAN, engineer, hospital, logistics, communications - very quickly the BG HQ gets overwhelmed. Furthermore the logistics sub-unit just wont have the people to support all of that. And that's just ADF assets. If you have US, UK, NZ or other allies you'll need a presence in the HQ, likewise DFAT, AFP, intelligence orgs, etc for non-ADF support.
Command: Related to above, the command a Bde brings is greater and deeper. A BG HQ will be no more than 20 people, a Bde will be about 100. That means there is sufficient expertise, the interconnections between Bde HQ and supporting/higher HQ are more solid and, critically, the deployed force can think about the next 7 - 10 days. The Plans Cell of a BG will be looking out 96 h at most, the Bde can do out 2 weeks. Means more time for prep and rehearsals. A Bde HQ also brings all the communications links of a Signals Regiment. Sure, a BG can (and does) borrow dets and Tp's from the CSR, but they can't use all of the C4 nodes and networks.
Authority: Intrinsically related to above, a Bde HQ will have a 1 Star running the show, a BG has a LTCOL. Now LTCOL's are magnificent creatures, brave, bold, devastatingly attractive - but they (a) don't necessarily have the ability to look wider (see Bde staffing), not the authority to use certain materiel. For sensitive ADF assets (SF, long range fires, etc - even AAvn) having a 1 Star direct their efforts allows for better use. The 1 Star also brings significant diplomatic weight, meaning they can work with allies and partners, as well as having more Joint experience than a LTCOL, hence working better with the Joint Force. The last point is important - why 1 Star and not BRIG? Because a Bde HQ is set up to provide a Minor JTF HQ capability, reserving DJFHQ for larger operations if needed. A BG just cannot.
Tasks: A BG is, by definition, a task orientated force designed for a specific mission. As soon as that mission is done, the BG structure is obsolete. Yes, we talk about common BG structures (inf-armour, triangle/square), but it really depends on the mission. This means if you send a BG, it can do one mission. A Bde on the other hand, it can reorg on the fly, raising and disbanding BG from a number of subordinate units to match any mission. Modern war is still defined by ideas like the 3 block war - meaning that you might be fighting and aiding at the same time. A BG simply cannot - undermining the overall Australian strategy.
Reserves: A Brigade, at worst, will bring 3x BG with it. Assuming the bare minimum (for BG size's, see How many IFV? and How many Tanks?) that's 14 tanks and 40ish IFV. Which isn't too bad - but what do they do after the first attack? Noting that any modern fight means we do an assault and face a counter attack (two fights) or do an assault and fail - which in turn means losses. So what do you do the next day? Say the BG looses 2 tanks and 4 IFV (and I'll be generous, not K-Kills), the EME peeps (devastatingly handsome, super smart, Gods and Goddesses who walk the world they may be) simply won't be able to repair them in time. So - you just wait? If they are K-Kills, how do you replace them? And the people? A Bde has options, they can rotate BG around. And remember, we'll try and throw a BG at any enemy concentration of ~100 - 120 people. If you've thrown an armoured BG into the mix, chances are you are facing more than 100 people.
Response to the unexpected: Surprise and deception work both ways. A Bde allows you flexibility. If the threat axis changes you can throw your reserve BG at it while you reorientate. Or reinforce your main effort with another BG. You can rapidly re-role a BG to conduct HADR because a cyclone just hit your SPOD while maintaining pressure on the threat with another two BG. LTCOL (see above - awesomeness in a single package) can do a heap with a BG, but easier to spread 2000 people over the task v 600.
Geography: You don't plan on really operating beyond your enablers (combined arms rules) meaning a BG can operate as far as an 81 mm mortar, or maybe an M777. That's not very much area, not really. If there is any urban areas in that AO, it's going to get much smaller - cities suck up forces like a sponge. A Bde can operate much further - over 100s or even 1000s of km if needed. A single BG hanging out overseas doesn't really achieve much. Have a look at our efforts in the MEAO which, will argumentative and having many other restrictions, shows a BG doesn't do much.
To summarise all of the above, INTERFET provides the best example. Three (simple) tasks: restore peace and security in East Timor; protect and support UNAMET in carrying out its tasks; and facilitate humanitarian assistance operations. All in a small nation (6x smaller than Tasmania) that had negligible threat. We put 8 - 10 BG into that, all gripped up under 2x Bde HQ and 1x Div HQ. It was messy from a C2 point of view for alliance and political reasons, but it shows just how quickly BG get absorbed. And that doesn't include the enablers that were also needed.
Bde HQ are our unit of action for many reasons. And as the loggie who was responsible for a CSR/Bde HQ a few years ago - even most of the Army doesn't fully understand what they bring. They can get bloody big, bloody quick, and as brilliant as LTCOLs are, they just cannot. The question that should be asked is what Bde will explicitly do what missions demanded of Army (and, as an aside, this should be demanded by the public as evidence we can do what y'all pay us for) - and is there a role for Div HQ? (#spoilers - **** yes)
