So unremarked has been the occasion that Kathleen has already been pulled to the surface up a deep shaft on the harbour's edge at Blues Point,on the lower north shore,and barged back to where she began her journey at Barangaroo,on the western edge of the CBD.
In the coming weeks,the 130-metre boring machine will start on the second parallel tunnel.
The twin kilometre-long tunnels under the harbour are one of the most complex parts of the second stage of Sydney's metro rail line from Chatswood to central Sydney,and onto Bankstown. The first stage from Rouse Hill in Sydney's north-west to Chatswood opened in May.
Sydney transport planner Mathew Hounsell said the use of a specialised tunnel boring machine to bore under the harbour was a"very significant"engineering achievement.
"It is a significant milestone in Australian history. It demonstrates that we are capable of delivering major infrastructure projects like other countries - but it is not a world beater,"he said.
He cited the 57-kilometre Gotthard tunnel under the Swiss Alps – the world's longest and deepest rail tunnel,which opened in 2016 – as an example of an extraordinary engineering feat.