What I see:
1) SH cannot replicate what F-111s can do as long range bombers.
2) SH is an overpriced plane with exaggerated abilities.
3) Australia had a good industry centered around the F-111, so even with the expenses, money was going back to the Australian people.
4) Australia is technically proficient to keep F-111s up until they get the F-35s.
Okay, here come some answers...
1) Wrong
2) Wrong
3) Wrong (see #1)
4) Wrong (see #1 again)
Now to expand on this, and really have it understood, one needs to understand that package delivered is both conducted and opposed at a system level, not a platform level. Unfortunately, the continued interest in the F-111 is only looking at some raw performance specs of the platform, and not where or how it performs as part of the overall system.
Now, here are some brief specs for the F-111, and then their irrelevance will be demonstrated.
Crew: 2 (pilot and weapons system operator)
Maximum speed: Mach 2.5 (1,650 mph, 2,655 km/h) at altitude
Combat radius: 1,330 mi (1,160 nmi, 2,140 km)
Capacity of 31,500 lb (14,300 kg) to carry combinations of bombs and stores
These are the metrics most platform fanbois tend to focus on, without any examination or understanding of the relevance.
Now, a high max speed of Mach 2.5 is good, but most modern air to air and even many air to surface missiles have speeds of Mach 3+. Which means that the F-111 needs to be able to evade detection, either by not being picked up by hostile sensors, and/or being able to deploy ordnance from outside a hosile's engagement range.
A combat radius of 2,000+ km is a good, long-legged aircraft. However, in order for that capability to be useful, there has to be (1) potential targets within that range, and (2) the aircraft needs to be capable of penetrating the airspace to get close enough to engage the target(s). Which puts one back to the point above about hostile SAMs and air to air missiles.
Now the third point, 31,000 lbs of ordnance is a great deal of ordnance. More than current roughly fighter-sized aircraft can deploy. However, the F-111 at the time of retirement was only able to employ 'dumb' and laser-guided gravity bombs as well Harpoon Block I AShM's IIRC and CBU's. Which means to carry out non-maritime, strike missions the F-111 would need to be able to get close enough to be essentially 'over' the target. Which in turn points back to the two previous points.
As things stand now, the F-111 which was designed about 50 years ago to penetrate enemy air defences with a high speed, low altitude, terrain following flight profile. Such a profile is now no longer sufficient to safely and reliably penetrate current air defences. Through to development of IADS, and the associated sensor networks, a low altitude flight path is not going to guarantee radar avoidance. More radar systems exist now to provide better coverage, and there has been a marked growth in the employment of airborne radar surveillance. Further, GBAD systems are much more advanced than they were in the early 1960's, and with the development of MANPADS which could result in multiple Mach 3+ missiles being sent inbound on an F-111, a terrain following flight profile is no longer a safe option.
This means that to conduct a strike mission, an F-111 would need to fly at altitude (~20,000+ ft) to avoid ground/trashfire. This puts the F-111 well within the normal detection and interception area of hostile fighters. Given that the F-111 was designed as a strike aircraft, not a fighter, the best it can mount vs. aircraft IIRC was a pair of AIM-9M Sidewinders and a 30 mm cannon. All of these are only useful WVR, and the F-111 needs to be nose-on to the target aircraft. Given that modern fighter aircraft have BVR missiles and nose-mounted FCR, the F-111 would not be in a position to defend itself against hostile fighters, thus requiring a fighter escort to penetrate hostile or contested airspace, and limited the F-111 engagement range to the combat range of the fighter escort.
Further, the ~31,000 lbs of ordnance as mentioned is basically stuck to being at best, LGBs. The newer and more advanced PGMs and stand-off munitions are not available for the F-111, as the avionics and wiring harness is too old to be compatible. While it is technically possible to develope a modern avionics package (including self-defence systems) for the F-111, such an endeavour would be risky, costly, and time consuming. Once such a package was developed (if it could be done successfully...) in order to install it in all the F-111's in RAAF service would essentially entail dismantling the F-111's to remove the old avionics and wiring, installing the new equipment, and then reassembling the aircraft. Again, all risky, costly, and time consuming. One also must remember, all this work would be done on an aircraft of which the RAAF has been the sole operator of since the F-111 was retired from USAF service in ~1998, and which had been out of production since ~1976, when the F-111F, the last production model, ceased manufacture. In other words, parts are scarce and if available are decades old. Otherwise parts need to be custom ordered for new production, and tooling does not exist to make the needed parts. Not to mention that the materials and metallurgy usable now is not necessarily the same as what was used in the F-111 when first produced.
So, do you really think it worthwhile for Australia to run a crash upgrade programme to extend the lifespan of a nearly 50 year-old bomb truck, which likely would not result in operational returns from the F-111 until the F-35 was itself already entering service, and would cost a great deal of money and trigger further stretching of the legacy Hornet fleet?
OTOH the F/A-18F SHornets which the RAAF will be receiving are advanced fighter/attack aircraft. They are capable of self-escort, able to engage and defend themselves against hostile aircraft. Due to the advances made in their avionics, they can provide better information on the battlespace than the legacy Hornets are capable of, and due to the level of sensor integration, gives the RAAF an idea of what is coming with the F-35, which means that there are paths to explore what the RAAF will be able to due to the F-35's avionics. Due to the greater range of the SHornets vs. legacy Hornets, plus the SHornet's ability to use standoff PGM's, the RAAF is regaining some of the strike 'reach' it used to have with the F-111, which was lost when the F-111 stopped being survivable in a modern battlespace without the legacy Hornets acting as escorts.
So, this is not just about Australia's ability to maintain the F-111, though the risk, cost and time involved did become the final nails in the coffin of the F-111, it was just the fact that the F-111 could no longer realistically escape detection or evade hostile aircraft in a modern battlespace.
-Cheers
