Object could only be seen through a Starlight Scope (infra-red device)

UFO Report November, 1969 Camp Pendleton, CA  While attending Scout/Sniper School for the Marine Corp I was witness along with at least 30 other Marines of a UFO.  This occurred during our night training on the firing range using Starlight Scopes.  This night was a clear night but without a moon.  The background in the distance was the mountain range on Camp Pendleton.  During the firing practice everyone who was firing using a Starlight Scope became exited by a bright light they could see through the scope.  The light was flying/hovering fairly low to the ground in the distance.  The weird part was that you could only see this light using the Starlight Scope.  With the naked eye you saw nothing; no light whatsoever.  Through the scope the light was obvious and moving over the horizon.  My recollection of this event would have been over a 30-90 second time period.  I looked at least 3 times through the scope to observe the UFO then with my naked eye and could see nothing.  I was watching through the scope when the bright object went around one of the mountains and came into view again from a valley.  The object began to rise into the air higher and then disappeared into the sky in a streak of light similar to a falling star but away from the earth.
Witness indicates that date of incident is approximate.  PD