A pair of enormous tunnel boring machines will soon begin their long journey across the Atlantic Ocean, destined for downtown Toronto, where the mega machines will eventually carve out the tunnelled portion of the much-anticipated Ontario Line subway.

It has been a big year of milestones for the 15.6-km, $27 billion rapid transit line between Exhibition Place and the recently-shuttered Ontario Science Centre. The biggest one yet came in November, when Metrolinx announced the start of work for a launch shaft where the line's six-kilometre tunnelled portion will begin at the future Exhibition Station.

On Friday, the regional transit agency offered up a look behind the scenes at the huge tunnel boring machines (TBMs) that will etch out the first major subway tunnel constructed through downtown Toronto in more than six decades.

Meet the newest member of our TBM family! This “newborn” – measuring in at about 7 metres wide – is currently undergoing testing in Germany. In 2025, it will embark on a journey across the Atlantic with its twin, ready to dig its way under Toronto’s downtown core! pic.twitter.com/qMsqX2eext

— Ontario Line (@OntarioLine) December 20, 2024

Official social media counts for the Ontario Line shared photos of "the newest member of our TBM family," referring to the gargantuan seven-metre-wide machine as a "newborn" currently undergoing testing in Germany.

Metrolinx has turned to German tunnel boring machine manufacturer Herrenknecht AG to supply the twin TBMs that will soon be launched to begin tunnelling on the line

TBMs being used for the Ontario Line are equipped with Herrenknecht's "mixshield” cutter heads, which are designed to chew through "heterogeneous ground" like sand and gravel, and is capable of performing under conditions like high water permeability and water pressures.

Once the TBMs are fully tested, they will be dissembled and shipped in parts across the ocean and delivered to the launch site in Toronto for reassembly.

Meanwhile, preparation work for the 16-metre-deep launch shaft the TBMs will eventually be lowered into has been underway since mid-2024.

When the shaft is complete and the TBMs delivered, the machines will begin their underground journey eastward, carving out approximately six kilometres of tunnels before emerging at an extraction site and future train portal near the Don River.

Stations along the route are also being prepped for the arrival of these TBMs with ongoing excavation works at future station sites like Moss Park and King-Bathurst.