UFO Sighting in Columbus, Georgia on April 15th 1973 – large disk very bright but i could not see the source of light

I was on guard duty at fort benning ga. We observed a bright disk I would estimate from 175 to 200 feet across it was no more then 500 feet in the air made a low pitch humming noise. It passed almost directly overhead we seen it just a few minutes because it was not very high..When we were picked up at the end of our tour we told the officer what we observed a short while later we were warned not to document or say anything about what we observed or we would be transfered to a high risk station where the chances were high we would not get home. The other guard who was with me was so nervous he crawled under a truck and stayed there until the object was out of sight. I don't remember exact dates I remember we were guarding a fuel depot during the fuel shortage 1972--73. We were armed..I also remember the name of the other guard..It has always bothered me that we were threatened and I do believe it would not of went well if I had persued it so I kept quiet..helecopter gun ships passed by a few minutes later I have no idea of the outcome of their persuit....Dave