V. Berlioz
Newbie
I recently came across this NIJ document dating from 1971 containing two Level IV ceramic solutions from way back in the day, which are the AVCO PA-500 and the KT-1. It's quite interesting to see how far the industry has come since then. The document sure makes for a good read.
https://www.ncjrs.gov/pdffiles1/Digitization/000608NCJRS.pdf
https://www.ncjrs.gov/pdffiles1/Digitization/000608NCJRS.pdf