On the jets: yes, at this point in time they're going to be kept in the hands of China, Spain and the US. The general presumption being that these three nations are the only ones with the industrial capacity to produce them. But when it comes down to China they pretty much technically stole the tech from the US. They went through an engagement with the US over the Philippines in the 70's during which they managed to shoot down a few US planes, then dragged the wrecks back to mainland China and duplicated what they could restore.

As it technically stands the theory and even the design of jet aircraft exists. The concept came up in the late 19th century actually, but was unsustainable because no country at the time had the knowledge of, or production capability to produce the high-temp steels or metals needed to do it. In this timeline much of what would have been the center for this sort of development (Europe) suffered so much from the Great War and post-war effects and general instability that any funding or industrial capacity put towards development of these things was crippled or became nonexistent. In this regards Spain was able - in theory, unless Googer says anything - was somehow able to take advantage of the situation and spring board its way to being "almost US tier" (if not that) and get the capacity to do jets. The US was left industrially intact and could pull it off. And China running on potential just tears apart corpses and remakes it.

So that explains that if it needs it. Of course, the proliferation of this technology comes down to the willingness of any of them to share and the willingness of any party potentially tipping the balance of power with distributing these weapons.

OOC we were just tired of the Top Gun try-harding and Gorgen said it's what he wanted when he set off. But let it happen when it happened. So we all voted to retcon out Jets as the backbone of an air force.

The same logic as with jets applies to computers and nukes. The historical divergence and all of that would have lead to either the deaths of key RL figures to delay or stunt growth in these sectors. And any and all economic and social damage as an effect of the Great War and the post-war rippled out to discourage funding in these areas in the name of austerity.

For guns, vehicles, and all of that then the common line of questioning goes something like this: Did it exist in the period? If yes, did it rely on computers in anyway (battleships, tanks, aircraft, etc)? If yes, did these computers take up a warehouse? If yes, it can be done. Alternatively you could replace instances of "computer" with "transistor" and basically have the same effect, canceling out a lot of radio technology and over-all effective radar and other guidance technologies. And that's sweeping through the surface.

But things like fax technology exists, since that was developed out in the 19th century and not strictly reliant on computers. So it's still possible to fax some things. It'd just be really slow and rudimentary.

I'm sure Vilage and Googer might have more to add to this too if either one of them steps in. But beyond sort of "game-y" explinations it can be styled as: Spitfires are cooler than F-16's.