Enigma Machine
Invented by Arthur Scherbius in 1918, adopted by the German military in the 1930s.
Each keypress advances rotors, creating a different substitution for every letter.
The plugboard (Steckerbrett) swaps pairs of letters before and after the rotor stack.
Over 158 million million million possible settings. Broken at Bletchley Park by Alan Turing and colleagues, a feat that shortened WWII by an estimated 2 years.