Could the R&D budget be hiding procurement of classified airframes? Seems odd that it would grow so much over the ~last 15 years.
You know what else has grown so much over the last ~15 years? The cost of literally every single required input into any sort of serious research, development, or engineering project. Labor, parts, materials, analytical equipment, services, prototyping, consumables, high end talent, etc. The real increase in costs to achieve anything in these fields is nothing remotely as modest as the inflation rate.
136% over a decade sounds like a lot of budget growth. In reality, that's only ~10% growth per year across the decade. When I reframe it like that, it doesn't sound so crazy anymore does it? Plenty of people's 401 (k) even outperforms that. Hell, the real growth in cost of living if you include raising a family, education, daycare, etc. has easily exceeded that by a mile.
There's no secret air/space fleet, secret nuclear super weapons, secret WMDs, or secret hypersonic missile arsenal. Those things cost not tens of billions, but trillions to put together. Not something you could hide within a $46.4 billion dollar 2026 budget that was less than half that 10 years ago.