Yeah, DARPA funded OpenBSD development in Canada in the past, so, not much surprise that they also fund research at the University of Cambridge, I guess.

https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/

The web-page itself makes no mentions of DARPA or AFRL, but if you click on any of the papers, the notices are all there.

P.S. ARM is HQ'ed in Cambridge, so, location-wise, probably a lot of talent that can do these kinds of things there.