Craft was seen at about 22:00 hours in the combat area none as I Corps. This ia about 50 miles outside of Da nang. The craft was hugh. there was no sound other than a rushing wind which reached the ground. The craft was heard 5 min. befor it reached us. It was a clear moon light sky was easily seen. There was no lights what so every. we were all armed yet not a shot was fired. The craft was clearly in our free kill zone. It was traveling no more than 5 to 8 miles per hour and was about 200 feet off the ground. it was reported to the officer in charge who said forget it we got other things to be concerned with. this is the first time I have reported this oyher than the night it happened. The craft was about 75 feet in diam.