for now I will just reiterate that the way the Doppler and GPS system data is combined to drive the Horizontal Situation Indicators (HoSIs)
but it is quite another thing for the handling pilot to be able to keep on track by reference to his HoSI when cruising at speed on a long leg with no clear visual landmark to aim for nor any ground feature beneath him (road, river, etc as they were over sea) for him to correct for drift – he needs his HoSI over sea with a fuzzy mass ahead of him
But Walter they don't, as usual you don't have a complete grasp of how the Chinook HC Mk II and its systems work.