Soft face is exactly what it says, it’s got soft rubber faces, basically just a shrunk down rubber mallet. Use it on things you don’t want to leave marks on.
Double peen is basically just a soft face except one side is like a hard epoxy like material. Harder than the rubber side, still softer than a metal head would be.
Wounded Knee (the second one not the original one) was 1973.
Kent State in '70. The Bonus Army (homeless WWI vets) in the 30s. Blair Mountain (coal miners on strike) and the Tulsa Race Massacre in '21.
Only a half dozen times in the last 100 years or so.