A significant portion of the defense spend is STEM. It takes a lot of engineering to build a bomb. It takes a lot of math to create/break encryption....
That just makes things worse. Imagine if most people working on nuclear reactors in the navy instead spent the time building and maintaining civilian equipment. The kind of people designing and building the F-22 etc where capable of more long term useful activities etc.
The US could be safe spending 1% of its GDP on defense and largely importing foreign weapon system designs for local manufacturing. There’s clearly a lower limit, but half of current spending is perfectly reasonable starting point before decisions get tricky.
Is there really that much overlap or are the budgets just so insanely high you end up with accidental overlap? Seat belts are a perfect example where the military and non military application was quite different on day one. But, military had the budget so John Stapp made the argument around how many pilots died driving in their civilian lives. Definitely a huge public benefit, but from what amounted to military funding of civilian research.
Packet switching saw first implementation outside the US including some key ideas like a router. We ended up with the ARPANET > Internet story everyone is familiar with more as an accident of history and a dash of propaganda rather than something that required US military participation. https://en.wikipedia.org/wiki/NPL_network
Teflon is another one people bring up as coming from the military but was invented accidentally outside the military long before its use in the Manhattan Project.
> largely importing foreign weapon system designs for local manufacturing.
I'm pretty sure they legally can't "largely import foreign weapon designs". The Berry and Kissel amendments, not to mention ITAR and a few other regulations, put a strong incentive on in-sourcing when at all possible. The only exceptions are for things that are really hard to get domestically.
Which foreign systems? If US would’ve withdrew from cold war, half of Europe would be learning cyrylic now, and there would be few countries to import tech from. Not to mention engineers from the eastern block working for the opposite side.