They had five nines safety. Well, in the sense that Wernher von Braun asked each of his lieutenants in turn whether they could think of any reason the rocket wo

They had five nines safety. Well, in the sense that Wernher von Braun asked each of his lieutenants in turn whether they could think of any reason the rocket wouldn't work, and the reply went "nein, nein, nein, nein, nein". Wish I could remember the source of this joke.