"

Dubious addition
Caltrops are used inside some atomic bombs to center the uranium or plutonium ""pit"" inside the spherical tamper. The air gap allows the tamper more time to accelerate, which compresses the pit more tightly and leads to more efficient fission.
I find this to be very unlikely  for something as highly-engineered as an atom bomb, I'd think they'd use something purpose-built.  "