> Because you need those calculations to "pump" nuclear weapons. They are needed to calculate both the geometry to make fusion bombs possible at all and to calculate the effect of a given geometry. They are the reason US/Russia/China have the biggest and strongest weapons known to humanity.

We have a couple new nuclear weapon designs, but not really going for bigger or stronger. Just packaging.

We built the big powerful ones with 1960s computing.

Now, stockpile stewardship -- being sure that stuff will keep working without ongoing testing -- is a bit expensive in compute. You need early 2010s supercomputer power.

In other words, I strongly disagree that nuclear weapons are the primary driver of high-end compute.

> We built the big powerful ones with 1960s computing.

And they are radially symmetric and simply totally overpower the initial fusion reaction, and that gives a secret number of solutions (>=1). But they sucks for many reasons, they're overpowered, heavy, and brittle and that is something we can "improve". And if you calculate the theoretical lower limit of device size for a given yield, you'll stop sleeping well.

And what do you need to approach that lower limit? Explosion simulations that are incredibly precise for a large number of different 3d shapes. And ironically the solution to the lower limit will also let you make the biggest yield devices.

Physically smaller bombs, with bigger yields. All you need is the correct shape (well, no, in practice there's no end to other things. Having the shape does not mean you can make it, for example, but it is the difficult part).

Hence the calculations, and hence the blank check. Not having the biggest ones

High end compute also existed in the 60’s.

The military has already mastered fusion (power), and likely has mastered gravity in some form in secret. They aren’t using mainstream compute for these discoveries