My son told me the following story about a year ago:
Ernst Udet was the second highest-scoring German flying ace of World War I, with 62 victories. He was second only to Manfred (Baron) von Richtofen, who had 81, but died in 1918.
Early in his career, Udet encountered Georges Guynemer, the famous French ace, in the skies over Lierval, France. A dogfight ensued, with each man trying to gain the other's back. (In those days, the singleseaters the two men favored could only fire forward, not backward, so to win each needed to get directly behind the other's plane.)
Udet knew from the start that he was in the fight of his life. Guynemer (whom he recognized from the "Vieux Charles" printed on the wing of his plane) knew all the tricks that Udet did, and both men executed many of the evasive turns, loops, rolls and glides which had made each of them so successful up to that point.
Finally Udet got Guynemer's back, and pulled the trigger of his machine gun. Nothing happened. The gun was jammed.
At this point Udet realized that he had to pretend to keep fighting, or Guynemer would just get behind him and pick him off. So he continued to roll and spin as best he could. But within a few minutes, Guynemer was able to get his back.
At that moment, with the Vieux Charles directly above and behind him, Udet knew that he was a dead man.
But Guynemer did not shoot. Instead he just pulled even with Udet. When Udet looked over, he saw Guynemer salute him through the cockpit window, then fly off.
The two men never spoke, and Guynemer was later killed during the war.
People later speculated that Guynemer's gun might have misfired as well. Udet remained convinced till the end of his days that the Frenchman had spared his life because he knew that Udet would have bested him but for the jammed gun, and couldn't bring himself to kill his opponent in what would have been an unfair fight.