One of our members wrote me about the origin of this expression.  It
emerged during or after the Great War, when one of the popular American
songs was, "Keep Your Head Down, Fritz-y Boy", and the American soldier
called the German soldier "Fritz".  After the war the German economy was,
understandably, rather a shambles, and so when something didn't work it
was "On the Fritz".  It's also related to another old expression, "on
the blink", as when Edison's Electric Light failed and went kaputt!

I wonder what picturesque expressions like this are in the German and
French languages?  (What names did the German and French soldiers have
for the British and American troops?)