I spent more time than is good for me on ADS-B last night mesmerised by a RAF C130 out of Brize appearing to fly VERY low over Sussex and Kent; the altitude at times showed as 50 feet, although more normally between 100 and 250. It flew out over Margate and between the windfarms into the North Sea, still low until eventually coming back in over Norfolk and climbing to 10,000 feet - at which point I went to bed. If the altitude readings are anywhere near correct then a number of Sussex and Kentish folk are going to have had a rude early morning awakening last night. I'm almost jealous I wasn't one of them!