The WC-135 Constant Phoenix has launched from RAF Mildenhall earlier today for a mission towards northern Europe and the Barents Sea. Interestingly, an RC-135W spyplane has launched from the same base on the same route. What’s their mission?

https://theaviationist.com/2017/02/22/u-s-wc-135-nuclear-sniffer-airplane-has-left-the-uk-heading-towards-norway-and-the-barents-sea/