A SPY ring, perhaps answering to China, may have stolen confidential files on the business model of Nissan's new electric car, the Leaf. Or so says the carmaker's boss, Carlos Ghosn. But The Economist has been allowed a peek at the technology under the hood—literally. We recently visited the factory, an hour outside of central Tokyo, where the eco-friendly cars are being built.

The Oppama factory employs around 2,100 workers. The workers’ average age is 42 and each of them has worked there, on average, for 22 years. About two-thirds of the workers are classic, full-benefit company employees who have been trained carefully and now enjoy perks, while the rest are part-time or contract employees, mostly in non-manufacturing, support-staff roles. The carmaker’s practice of maintaining skilled employees—so unlike electronics manufacturers, who tend to hire temps—helps explain one of the Leaf's most interesting, behind-the-scene features: it is somehow bolted together on the same assembly line as three other Nissan models, cars with conventional, internal-combustion engines.

The right parts are delivered to each production stage with the co-ordination of sophisticated computer technology. Yet it is the skill of these seasoned workers that enabled Nissan to add the Leaf to the existing line. Electric vehicles (EVs) have far fewer parts, and many stages in the process of their assembly are entirely different. So the line workers need to work differently. Battery bays are spread along the chassis and beneath seats; the small motor is popped gently under the bonnet at the same time as seat-belts are attached.

That said, adding a very different type of vehicle to an existing assembly line may be one of the reasons for the slow ramp up of Leaf deliveries. Nissan plans to make 50,000 Leafs (“Leaves”?) in Japan this year, and to start production at other factories in Europe and America. More than 20,000 American customers are stuck on a waiting list: Nissan shipped barely 100 Leafs in December and January combined. This hasn't stopped it from posting ruddy results. This week Nissan reported that sales grew 19%, to ¥6.4 trillion ($74 billion), over the past nine months and that its operating profit almost doubled, to ¥448 billion.

The Leaf's core technology, the battery, is handled by Nissan alone. Sales in Japan have been fuelled by a generous government subsidy on green cars, which in effect lowers the price from ¥3.6m to ¥3m (around $35,000). When that buyer’s incentive expires later this year, the car may have a tougher time competing domestically.

The best part of such factory visits? Not the sights but the sounds. In the accompanying video, be sure to listen to the fantastic industrial cacophony of metal-bashing carmaking, accented by the high-pitched digital melody of the automatic trolleys that deliver parts to the line.