When A Bicycle Courier Saved The World:

From The Gallup Management Journal (behind paywall) , by way of thewashcycle.com :

"The Cuban missile crisis in 1962 not only showed how close the United States and Soviet Union could come to a nuclear war, but also the sorry state of the communication channels needed to avert it. During one point in the crisis, the Soviet ambassador to Washington had to rely on a bicycle courier to take his urgent messages for Moscow to the local Western Union office."