All these posts have been absolutely fascinating and I've learnt a lot. I was indeed confusing the various boats, I can see now the single boat on the superstructure

In comparing the Trident and ALK models the former seems to have an extended flight deck - for Lynx maybe? So if I want to have the ALK as in 1982 one of the Survey boats has to go (maybe)

Have just ordered a copy of Beyond Endurance by Nick Barker