Comment by LorenPechtel

You are describing salvage fusing.

When you're playing with nukes it actually is rather effective, not from a standpoint of chaff (you don't bring it) but the ionization of the nuke makes a radar blocked zone and the following missile is going very, very fast--makes a bunch of progress while the defenders are blind. It's also why we don't like nuclear anti-sub weapons--the dead zone lasts for hours, there's no way to know if you actually got the target.

But a drone is small and slow. You'll need an awful lot of drones to punch through defenses this way and the whole thing goes out the window when the laser pops drones farther back in line. And chaff only denies a small area and for a short time.