Engineers have begun assembling two giant tunnelling machines that will dig the final 4.5 miles of underground HS2 (high-speed railway).

Weighing at 1,250 tonnes, which is equal to nearly three fully loaded Boeing 747 airplanes, each of the tunnel boring machines (TBMs) will launch from an underground box at one end of the project's Old Oak Common station.

They are expected to take around one and a half years to reach the railway's final southern terminus at London Euston.

As well as taking passengers closer to central London, the extension to Euston will create additional capacity on the new high-speed line, allowing more services to run to more destinations across the Midlands and the North.

In keeping with tradition, the TBMs have been given female names after prominent women in history.

One machine is called Karen after Karen Harrison, the first female train driver in the UK who was based out of Old Oak Common depot. The second is named Madeleine, after Madeleine Nobbs, the former president of the Women's Engineering Society.

The unveiling of the TBMs, the final set to be launched for the railway between London and the West Midlands, marks another significant milestone for HS2.

It comes on the day that Mark Wild joins HS2 Ltd as the company's new chief executive.

Mr Wild, former CEO of Crossrail, will help oversee the project's transition from a 'major construction programme to a working railway, with a renewed focus on controlling costs'.

Euston TBM Madeleine pushed into launch tunnel preparing to begin constructing the Euston Tunnel (credit: HS2).

Rail Minister Lord Hendy said: "I'm delighted to welcome Mark Wild to HS2 and look forward to working with him to successfully deliver Britain's largest rail project sensibly and efficiently for the benefit of passengers and taxpayers.

"The sheer scale of the progress at Old Oak Common – and the benefits we will realise from taking HS2 to Euston, as confirmed in the Budget - reminds us that this is a once-in-a-generation project.

"HS2 will not only improve transport links for millions but unlock huge potential for growth, jobs and regeneration right across the country."

The TBMs were manufactured in Germany by Herrenknecht AG and were transported to Old Oak in pieces before being reassembled on site.

This summer, the HS2 team lifted the machines into the underground station box using a 750-tonne crane. They are now being reassembled at the eastern end of the station, ready to bore to Euston.

HS2 explain that TBMs are like underground factories, excavating the tunnels using a turning cutterhead, lining them with pre-cast concrete tunnel segments, grouting them into place before moving forward at an average speed of 16 metres per day.

HS2's London tunnels contractor, Skanksa Costain STRABAG (SCS) is already well advanced with construction the Northolt tunnel – a separate structure running west out of Old Oak Common towards West Ruislip, outer London.

Unveiling of two giant tunnelling machines on the day that Mark Wild (left) takes up new role of HS2 Ltd CEO (credit: HS2).

The Mayor of London, Sadiq Khan, commeneted: "After so much uncertainty, it's great to finally be working with a Government that recognises the huge importance of this scheme to London and the UK, and understands why terminating HS2 at Euston is so important.

"It's exciting that these tunnel boring machines will soon be getting work underway.

"This is another example of the difference that the new Government's approach is making in London, delivering real benefits that will help to build a fairer and greener London for everyone and deliver the change Britain needs."

Huw Edwards, Stations Delivery Director, HS2 Ltd, added: "We welcome the commitment from the government to build HS2 all the way to Euston and preparations to tunnel from Old Oak Common are now well underway.

"A terminus station for HS2 in the heart of the capital will provide a vital gateway for passengers travelling to and from the Midlands and North, and will undoubtedly lead to the transport-led regeneration of Euston – supporting growth in the local economy and creating thousands of new homes and jobs."

Final plans for the future HS2 terminus station at Euston are still under review and HS2 Ltd is continuing to work with the Government and other stakeholders to design an affordable station design that can run HS2 services from London to the Midlands.

Further details will be announced by the Government in due course.

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