As a vision of the imminent future, it might strike a chill into Europhobic hearts: a German contraption measuring 140 metres (460ft) in length, designed to drive into the very core of the City within months.

Yet the unveiling of the first Crossrail tunnel boring machinemarked what should eventually be a very British achievement: a major new rail line across central London from Heathrow airport through to the east, one of the biggest current engineering projects anywhere in the world, providing jobs and economic stimulus.

For now, though, the starring role belongs to the machines in the small town of Schwanau, in the south-western state of Baden Württemberg, at the growing global headquarters of Herrenknecht, which is prospering as the manufacturer of more than half of such monsters worldwide.

Eight of these £10m moles have been commissioned for the 13 miles of tunnel: six designed to cope with the London clay from Royal Oak in Paddington in the west, and two for the chalk in the eastern stretch down to Woolwich.

"It's not so much a machine as a mobile factory," says Roy Slocombe, Herrenknecht's UK director; a factory with a canteen and toilets for the 12-hour underground shifts as work goes on around the clock. The machines are fitted with a decompression chamber for anyone drawing the short straw of having to climb into the very cutting edge for emergency repairs.

Behind a 6.2-metre cutter head (in Crossrail navy and white) is a hydraulic arm. Massive chunks of earth are fed via a narrow-gauge railway along the interior of the machine, which is itself on wheels – a system that operates on the Wallace and Gromit principle of laying down a tunnel in front of itself as it goes, albeit much slower.

Via conveyor belts and pipes, about 6m tonnes of earth will eventually be funnelled out of the back to be transported away from London. Some has been earmarked to create a Royal Society for the Protection of Birds nature reserve at Wallasea Island off Essex.

The first machine will soon be reassembled in Royal Oak to start tunnelling in March through the capital's labyrinth of sewers and tube lines, plus Ministry of Defence bunkers (location and contents unknown). All tunnellers have to submit their routes for MoD approval. "It's like playing battleships," said project manager Andy Alder: planners only know if they have scored a hit, but not where.

Crossrail is at pains to stress that more than 95% of the £14.8bn outlay will be spent in the UK, on other machinery, construction and employment. More than 3,000 people are working on Crossrail and thousands more will be employed in the next four years as the main infrastructure work is carried out. Further jobs will be supported along the manufacturing supply chain.

A new tunnelling academy in Ilford, Essex, will train thousands in skills that will also be essential for impending works to the National Grid, Thames sewers and – possibly – the high-speed railway being planned between the capital and northern England.

Meanwhile, between the towers of Canary Wharf and Billingsgate, displacing the water from the dock, the first embryonic Crossrail station has already taken shape. In the bowels of this cavernous shell, four giant steel rings mark the spot where the machines will tunnel in, hidden from the eyes of City workers in the offices just above.

Michael Bryant, chief operations executive for Canary Wharf Contractors, claims a proud record of no complaints from their well-paid neighbours so far: Japanese hydraulics ensured the piles were driven almost noiselessly into the Thanet sand, he said.

Critics wonder if Crossrail will be a glorified tube. The six new central London stations from Paddington to Whitechapel are only five miles apart, but backers say the crucial question is not speed – although it will more or less halve journey times between Heathrow and London's employment, entertainment and business districts – but capacity. Up to 36,000 passengers an hour can be lifted off London's creaking underground system.

Crossrail's genesis has been, according to Tony Travers of the London School of Economics, a peculiarly British example of how not to get big infrastructure schemes off the ground, because almost 30 years will have elapsed from its political conception in 1989 to its current projected completion date of 2018.

Funding arrangements eventually struggled into place in George Osborne's 2010 autumn statement, although contracts for rolling stock and operators need to be signed, when more controversy is likely to ensue.