Large UFO over Mt. ILIAMNA Alaska.Driving westerly, uphill out of Homer Alaska, passenger spotted an object that was somewhat cloud-like but different in that it had a metallic sheen to it and it was in motion contrary to the other clouds that were nearly motion-less on the northern portion of the sky. Thus, the cloud condition was only partly cloudy and this object appeared to be at approximately 15-to 20,000ft and at least 3 miles distant to the clouds present when first sighted. The 'craft' traveled at a high rate of speed, climbing higher into the western sky that was relatively free from clouds over the "Cook Inlet". It was first noted to be about an inch long over head when first sighted; half an inch over the middle of the Inlet and about a quarter of an inch in length (over Mt. Iliamna), when one measures with an arm extended out using finger and thumb to bracket the object. This experience lasted 3, 5, minutes, no more. We have noticed many jet-liners, military transports flying in our skies day and night and basically comprehend their size relative to their flying altitudes fairly well since we are both military veterans, U.S.N., and U.S.A.F. This was MUCH TOO LARGE for anything published in Jane's--LOL!!!!! Think saucer section separated from Star Trek's Enterprise, leaving a cloudy vapor, (tear-dropped vapor shape that traveled with the craft).((NUFORC Note: Possible contrail behind a high-altitude jet?? PD))