HS2 has launched its second tunnel boring machine (TBM) in the capital which has begun its five-mile journey beneath London. 

Named after 18th century astronomer Caroline Herschel, the giant machine will now dig for 22 months non-stop - except for Christmas Day - towards Greenpark way in Greenford, boring five miles of the twin-bore Northolt Tunnel.

Caroline will be operated by a crew of 15 people, working in shifts. An additional 25 people will directly support each tunnel drive on the surface.

Travelling at an average of 14m per day, Caroline will dig the five-mile tunnel and install 4,207 tunnel segment rings to create the tunnel. 

The TBM is the fifth to be launched by HS2 and the second to get under way in London. 

The 2,000 tonne machine joins TBM Sushila, which was switched on earlier this month on the same West London site. Sushila is named after local schoolteacher Sushila Hirani, head of department and lead for STEM at Greenford High School.

TBM Caroline was switched on by HS2’s civils delivery director, Mike Lyons. 

He said: “HS2’s construction continues to gather pace, and the launch of the fifth Tunnel Boring Machine on HS2 is another significant moment for Britain’s number one levelling-up project.

“Creating jobs and contracts for businesses today, HS2 is an investment in Britain’s economic growth now and for generations of rail passengers to come.”

The machine was given the name Caroline after it was put forward by pupils at Brentside Primary Academy in Ealing, who were inspired by her contribution to astronomy whilst learning about earth and space in their science lessons. 

Caroline will be operated by Skanska Costain STRABAG JV (SCS JV), HS2’s main works civils contractor constructing the HS2 tunnels in London. She joins Sushila who has already travelled over 70m in the three weeks since launch.

James Richardson, managing director of Skanska Costain STRABAG JV, said: “We’re delighted to have begun our tunnelling journey towards Euston, travelling under one of the busiest cities in the world. 

“Getting to this point has been a huge team effort and the scale of this programme has enabled many new people to join the industry and work on this crucial national infrastructure project.”

Once Caroline and Sushila reach their destination at Greenpark Way, they will be dismantled and extracted from a 40m deep shaft.

Separately, two other equally massive tunnel boring machines will set off towards Greenpark Way from HS2’s Victoria Road site in 2023 to build a further 3.4mile twin-bore tunnel.

Combined, the quartet of TBMs will build 8.4miles of twin bored tunnels between West Ruislip and the new high speed rail super hub station at Old Oak Common. 

Another tunnel 4.5 mile twin-bore tunnel extending from Old Oak Common to Euston will complete HS2’s journey to its London terminus.