It seems that, late in the war in Vietnam, the CIA became displeased with the amount of cooperation they were getting from the South Vietnamese government. So, they decided to stage a coup, depose then-President Thieu, and install someone more to their liking.
A special field agent, code name “Jack,” was dispatched to meet with the Saigon bureau chief (code named “Santa”), and work out a plan. The plan was that the local agents (code names “Comet,” “Cupid,” “Donner,” and “Blitzen”) would lay the groundwork, bribing guards, setting up escape routes, and so forth.
Then, on a specified night, “Jack” would assassinate the head of the army, General Po, by releasing poison gas into the ventilation system of his residence. Following this, he would kidnap President Thieu, who was thought to have some value alive, and take him to the coast, where “Jack’s” partner, “Jill,” would be waiting with a boat to take them to an offshore submarine.
All seemed to be going according to plan. Then, on the very day the coup was to be carried out, one of the local agents was captured by the South Vietnamese secret police! “Santa” knew that this particular agent wasn’t very good at resisting torture, and would soon be screaming out all he knew. Knowing he had to work fast, “Santa” wrote up a special coded message, and had a courier get it to “Jack” immediately.
Luckily for the CIA, “Jack” received the message in time, so the plan was aborted, and a messy international incident was averted. The message “Santa” sent, after decoding, read: “Go to Jill. Go directly to Jill. Do not gas Po. Do not collect Thieu–Donner hollers.”