The Welrod, and the Brugger and Thomet VP9 which is based on the Welrod.
These are some of the quietest pistols ever.
The Welrod was designed for assassinating German officers in WW2.
The B&T VP9 is designed for humanely putting down animals without causing alarm and distress to other animals.
https://www.youtube.com/watch?v=o7tP9s4mm5I
As I understand it, the VP9 has been purchased by military users for the same kind of uses as the old Welrod.