It was heading towards the USA, jc, might have been out of Mildenhall but more likely the Continent I would have thought.
Ah, I recall the days when the C-5s and C-141s used their serials as call signs - MAC 40169, etc... Tho I did hear if they'd filed the paperwork and the assigned aircraft broke down, they changed to a different aircraft and flew the mission using the original call sign.
Cheers
Treadders