English: Excalibur was a proposed x-ray laser based anti-missile technology. It used a nuclear warhead surrounded by a number of metal rods that acted to focus the output of the explosion into narrow beams that would be aimed at nuclear missiles and their warheads. This image shows a single Excalibur exploding in the upper left of the image and firing at three targets. In practice, each warhead would fire at dozens or thousands of targets at once