Funny how I can look at the same set of circumstances and come to a completely different conclusion. Waiting for 6th gen aircraft to become available, even with an interim F-15X (which does not actually exist yet as far as I have been able to confirm it remains a proposal) or other 4th or 4.5 gen aircraft buy would IMO be a classic example of pennywise, pound foolish thinking, though TBH I doubt it would even be pennywise. At present, I am unaware of even any agreed upon characteristics for what would distinguish a 6th gen fighter from a 5th gen one. That strongly suggests to me that at least for the time being, any work on a "6th gen" fighter is taking place in discussion groups. In short, the situation is likely to be similar what was going on in 1981 where the USAF was coming up with requirements for a new air superiority fighter to replace the F-15. These requirements led to the Advanced Tactical Fighter (ATF) programme in 1984, which in turn led to the YF-22 and YF-23 prototypes and ultimately the F-22 Raptor which first entered service in 2005. More than 20 years after the ATF programme kicked off, never mind the capability requirements list which cause the ATF programme to be started with the RFI in 1981. Given that fighters like the F-35 are expected to see frontline service with the US until 2050 or later, I would anticipate any replacement programme that the US might have initiated already, to have a planned IOC some time in the 2040's. It might also be the case that the US does not currently have any real fighter programme running, and any noise people are hearing about is more theoretical ideas that some of the aerospace companies are toying with. Sort of like how some engineers at one point came up with a proposed FB-22 strike aircraft. This in turn raises some hard questions which would need real answers for. For instance, if the US does have a new gen fighter start entering service some time in the 2040's, would Canada or anyone else be able to purchase it? Keep in mind that by US law, the F-22 cannot be exported. If Canada was permitted to purchase this hypothetical replacement fighter, when would it be able to reach a sufficiently capable operating capacity to permit whatever active RCAF fighters were then in service to start being retired from duty and replaced? This would of course be dependent on what build slots Canada was able to get, as well as how quickly Canadian personnel could reach competency with the new aircraft. From my POV, there are just too many potential risks involved to plan on waiting until 2040 to get the 'next shiny new toy' which might not even be real. As for going with the F-15X... even with the proposed avionics upgrades it would still not have some of the capabilities inherent in a 5th gen fighter. I also found it interesting when I looked at the Boeing page which discussed it that Boeing made a point of highlighting the F-15's speed. As most people interested in defence matters should be aware of by now, the kinematic performance of fighters is of significantly less priority in terms of overall importance than other capabilities. A fighter with a pilot aboard who can withstand 12g turns is not going to be able to get away from a 60g-turning missile fired from within the NEZ, and a max afterburner speed of Mach 2.5 still would not be enough to get away from a Mach 4+ missile fired from within the NEZ. While a high max speed and acceleration can reduce the size of a missile's NEZ, I would much rather have a fighter with a significantly smaller RCS and heat signature, since those factors can dramatically impact the ability of hostiles to engage. As for the mission focus for any RCAF fighter replacements... They really should be multi-role fighters. If a much narrower focus like air superiority was selected, then they become inflexible and irrelevant for all missions except for those within their focus area. Given the small size of the RCAF, having such a limited capability could hamper the entirety of Canadian defences. A multi-role fighter could perform air intercept missions, ground attack/CAS, strike and maritime strike missions. Even if Canada were not to utilize them as such, a multi-role fighter could perform these roles in a training capacity so that Canadian Army and/or RCN personnel and kit could get experience working with such capabilities, or even defending against them if the fighters were used as an OpFor. We do not know what the future holds although I suspect there will be more conflict than we have seen in the past thirty years. With that in mind, I would much prefer that Canada get as much capability across a spectrum of potential threats as possible, rather than trying to defer doing so another 20 years or more into the future.