A Flash of light that lit the ENTIRE sky. It was NOT lightning !!!Standing in formation, 84 soldiers all witnessed a flash in the sky. The sky was clear and NO lightning was present although it could have just been an electrical disturbance in the atmosphere but I'm not really certain. The ENTIRE sky lit up. Usually when lightning bolts strike you can see a path but this was NOT a lightning bolt. The flash appeared for 2 seconds and vanished.All the soldiers in formation just looked at each other and scratched their heads.Although the area is in the flight path of aircraft landing at Frankfurt Internantional Airport, there were NO aircraft in the area at the time of the flash.