Lonewolf_50, you raise an extremely important point. It's one of the reasons that Block 4 won't just be a single upgrade delivered straight after SDD is finished. Each of the US Services and PNs need time to bed-in, but they won't have long. Will it be long enough? Probably, but when Block 4.1, 4.2, etc all start to roll in with upgrades from 2019 we'll need to be careful not to overmatch what the customers can cope with. It just creates confusion and takes jets away from the line constantly.