The Tornado GR.4 is not a CAS aircraft. Even though it may carry Brimstone, it's not particularly suited to the mission.
The strike mission in Afghanistan is already sufficiently handled, CAS aircraft are also needed however. The only other fixed-wing CAS aircraft in Afghanistan currently are the (8-10?) A-10 of the USAF 455th AEW operating from Bagram.
Strike aircraft:
- USAF: about 10-12 F-15E, Bagram
- AdA: 3 SEM + 3 Mirage 2000D, Kandahar
- NoAF: 4 F-16MLU, Kandahar (?) [to be replaced by Belgium in Sep?]
- KLu: 8 F-16MLU, Kandahar (?)
Recon and EW aircraft:
- USN: about 4 EA-6B + 1 EC-130H, Bagram
- Lw: 6 Tornado IDS/Recce, Mazar-i-Sharif
- AdA: 3 Mirage F1CR, Kandahar
Additionally, there are about 20 AH-64 currently in Afghanistan (US,UK,No).
You are correct in saying that the Tornado GR.4 was not designed for CAS. It can, however, do the job as has been proven during Operation Telic in Iraq and exercise Green Flag in the US.
There was a report in the UK aviation magazine
Airforces Monthly a while back stating the sterling job the GR.4 is doing in Iraq. Apparently many ground commanders prefer it, for several reasons, among them being the fact that it has good loiter time and is extremely accurate with Enhanced Paveway II and 27mm cannnon.
Like most strike aircraft today the GR.4 also carries a targeting pod and has an extremely important ISTAR role to fulfill in addition to CAS.
I believe the reason why GR.4 wasn't deployed to Afghanistan initially has to do with the fact that the UK government wasn't sure how long the deployment would last, they thought there was a good chance it might be short term. (As the then Sectratary for Defence stated - they might be home without firing a shot) Also they didn't know how demanding the deployment was going to be.(They initially only sent five or six GR.9's. There are now 11.) Thus they totally underestimated the impact the deployment would have on the three squadron GR.9 force.
Plus it must also not be forgotten that the runway at Kandahar was initially in bad shape. (Tailor made for STOVL Harriers.)
And also the GR.4 force was already doing the Iraq commitment. To sum up then.. a number of factors were at play.
We will almost certainly see the Harrier force relieved soon. Be it by Typhoon or GR.4 or both.