A Transatlantic Tunnel, Hurrah!

An alternate universe where America lost the Revolutionary War and is still a colony of England.
And Gus Washington ( descendant of our George) is building a tunnel under the Atlantic.
He is working with a descendant of Isambard Brunel (if you don't know about him you should)
and dating Brunels daughter.
It's a great story of a massive engineering exercise.
Lots of fun and recommended

But there is a part I didn't get.
Starting at both sides, they have built tunnels out from North America (Nova Scotia) and England (Wales) out to the end of the continental shelf.
But for some reason, it is vitally important for Washington to get from New York To London
so he can be on the first train from London out to the edge of the shelf.
So there is a crazy adventure involving going back and forth between Nova Scotia and New York, then a ride in a crazy helicopter that crashes, then (I think) into a jet airplane and then on a rocket and finally an ordinary train. All this involves extreme danger but I have no idea why it was important. Oh, and I think Washington has to jump from a speeding race car onto a moving train.