I was never a Shack driver let alone anything later, so my ignorance is massive. However the P-1 does look to me like a purpose designed aircraft. It has good visibility for the driver, it looks rugged, it has 4 engines, which seems good to me if you're way out over the water, and its not a compromise adaption of a civil aircraft (and they are always compromises to some extent). Surely going for something like the P-1 that is actually designed for the job from the bottom up would be better - and possibly more adaptable as technology changes in the future. I wonder if it could be re-engined by RR? Tay 611-8C - I don't know but its at least the same power and a long proven design.