While this is about the largest nuclear bomb ever produced, I also find the stories of the smallest interesting. Project Orion was a classified effort by the US to produce minituarized nukes for use in dropping out the bottom of a spacecraft to accelerate to insane top speeds.

Wicked pollution but I think they could also get to Alpha Centuri at like 10% c or something like that. Human-lifetime achievable. Project was cancelled for a number of reasons, the top likely being the Atmosphere and Space Test Ban.

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...