Should go back to the 1950s
I'm a little disappointed in DARPA. This project isn't nearly as bat-shit crazy as we've been led to expect - no cyborgs, no artificial intelligence and precious little danger - where's the fun in that. My benchmark in looney-tunes missiles is Project Pluto from the 1950s which even had a cool acronym - it was to build the SLAM (Supersonic Low-Altitude Missile)
Instead of boring old kerosene, SLAM would have had a NUCLEAR jet - essentially a completely unshielded nuclear reactor that heated and expanded incoming air to generate thrust. It's pure brilliance for anyone with a Strangelovian streak in their personality - it's a sort of Chernobyl with wings!
A SLAM could have remained airborne for months just waiting for Jonny Soviet to get all uppity, whereupon it would have screamed towards the Motherland at supersonic speeds before turning Moscow into hot slag - and it wouldn't even have needed a warhead to be a radiological disaster to remember.
They even built a couple of stationary prototypes, but before this Armageddon to Go was given the green light, the US decided to be slightly less mental and switch to ICBMs.
Come on DARPA, give us something Pluto mad so we can fall in love with you again.