Bright ball of light traveling straight up over Zirndorf, (West) Germany

The date is approximate, but was in February or March, 1975.  I was 20 years old and serving in the Army.  I was stationed at Pinder Barracks, Zirndorf, (West) Germany.  Zirndorf is a suburb of Nuremburg.
We had just finished our morning daily dozen and were running in formation when I noticed a very bright ball of light no more than 300 feet in front of me and about 500 feet up.  It was so bright it took several seconds for my eyes to readjust to the ambient light after it disappeared from sight.  I could not determine size or shape but estimate it to be about 50 feet in diameter.  It just appeared to be a ball of light as bright as the sun with no distinguishable shape.
When I first saw it, it was already moving straight up at a high rate of speed and disappeared in about 2 to 3 seconds.  I shouted, "Look!" and pointed toward it, only to be reprimanded by the sergeant in charge for talking in ranks.  
I asked a few people, but if anyone else saw it, they did not say anything to me.
Witness indicates that date of sighting is approximate.  One of several seemingly high-quality reports from the same source, who describes himself as a public employee, who had a great deal of responsibility.  We suspect tha the witness is a very good observer.  PD