I have two, both of which will date me as an old guy.
I heard this one when I was a boy scout in the early 70s:
A cargo plane is carrying three passengers that needed to be someplace in a hurry: Henry Kissenger, a priest and a boy scout. The pilot announces a major mechanical malfunction, that the plane is going down, and the passengers should grab parachutes and jump. The three passengers run back to where the luggage and the parachutes are all stored. The boy scout gets there first, and sees that there are only two parachutes. He picks one up and hands it to the priest, and says, "here father, even if I grew up to be 100, I'd never be as good a man as a priest. I'll stay aboard."
The priest says, "nonsense, my son, you are a fine lad with a long life ahead of you," and hands the bundle back to the boy.
Meanwhile, Kissenger grabs a bundle for himself, and says, "I am THE Henry Kissenger. I am the secretary of State. You two argue over the other chute, I am far too valuable to the world to die," straps in and jumps.
The priest shakes his head sadly, and says "take that chute and go with God, my son."
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I heard this one back when I was in the army toward the end of the cold war. I was told it was actually making the rounds in the Soviet War College.
An instructor at the Soviet War College is lecturing on the conduct of the defense. He sets up a hypothetical:
"Comrades, you have command of a Motorized Rifle Division. On your left is an American division conducting a fixing attack. On your right is a German Panzer division conducting a main attack. Against which force should you commit your reserve regiment and why?"
A student raises his hand and is called on. "I would release my reserve against the German Panzer division. It is the main attack, and, therefore, the main threat to my division."
"Wrong!" shouts the instructor. "You must attack the Americans. Very well, now let us suppose that the Germans have broken into your rear area. Do you counterattack the Germans or the Americans?"
Another student raises his hand and is called on. "Now the circumstances have changed, we must seal the breach in our defense, we must counterattack the Germans."
"Wrong!" shouts the instructor. "The Americans! You must always attack the Americans first, comrade."
"But why?" asks a student. You are telling us to always attack the Americans before the Germans. Why?