The last rumour that I heard about MRA4 is that it might not even carry a sonobuoy for a bit, let alone "every weapon in the RAF arsenal"
The use of MR2 to do less than 30% of what an MQ-9 Reaper can probably cost the lives of 14 good people. Also, the EO/IR turret fitted to MRA4 is less capable than the one on MR2 (because it was asked for in 1997!). See link
Northrop Grumman Night Hunter Electro-Optical Surveillance and Detection System (EOSDS) / Night Hunter II (United States) - Jane's Electro-Optic Systems
The apeture of Night Hunter is 11 inches, MR2 had the MX15 which is 15 inches and Reaper has MTS-B, which, according to Raytheon's website, is 22 inches. Simple comparison of apetures would show that MRA 4 would need an upgrade to offer anything of value in Afghanistan.
The weapons release trials would cost millions and then there's the cost of flying such a large aircraft over Afghanistan. Sorry mate, but MRA 4 over Afghanstan is a "barking" idea (IMHO)!!
6hrs of "on call" CAS - try 12-14hrs and then you're in business (or just use Reaper).
Finally, 2 seat Typhoon has even less internal fuel. So I very much doubt if the RAF are looking at 2 seat ops.
LJ
