A soldier, a sailor and an airman were sitting together having a beer and they begin to discuss the greatest technological inventions of the modern world.
"It is the laser," said the soldier, a man of obvious superior intellect.
"The laser, because with it, you can determine the precise range to an enemy target, you can use it to gather important telemetry information and you can even use it for photography that is almost tri-dimensional."
"No," interjected the sailor, also an intelligent person, but obviously standing in the shadow of the soldier's phenomenal mind.
"It is the radar. With a radar you can track incoming aircraft and missiles, you can determine the speed of the particular vehicles that are approaching your ship and, if you use it right, you can even heat your lunch."
"I disagree," said the airman, a man of, well he's an airman and all airmen are borne out of a diminishing gene pool.
"The greatest invention is the thermos."
"The thermos?" exclaimed the other two.
"Yup, a thermos," he said. "I mean, just think about it.
If you want something hot you put hot stuff in it. If you want cold, you put cold stuff in it."
"Yeah, so?" quizzed the other two.
"Well," said the airman, "How does it know?"