The USAF appears to run regular trips to/from (I'm guessing) the States to Ramstein AFB in Germany, using a C17 transport. You won't see it on FR24, but it is often visible on the unfiltered display at ADSB Exchange. Through binoculars it has a distinct "dumpy" appearance compared to civil jets such as the B747 & A380. I have seen it several times over Norwich, tracking roughly E/W, and it's normally at around FL300.