Gallons of ink have been spilled describing how DARPA works, but in a nutshell here is how DARPA works.
Around 100 program managers (PMs) with ~5 year appointments create and run programs to pursue high-level visions like “actualize the idea of man-computer symbiosis.”
In these programs they fund researchers at universities and both big and small companies to do research projects of different sizes. Collectively, groups working on projects are called performers.
Top-level authority lies with a Director who ultimately reports to the Secretary of Defense. https://benjaminreinhardt.com/wddw