Each day, more than 150 white buses fan out on the black tar roads that run through the outskirts of the Indian city of Chennai, ferrying workers to a factory run by the Taiwanese manufacturing giant Hon Hai Precision Industry Co., better known as Foxconn.

Although calling the facility a factory doesn’t quite do it justice. It’s a 160-acre fortress lined with assembly shop floors, testing and storage rooms, nine hostel towers, huge parking bays, and a power station.

Roughly 40,000 employees work through three shifts, under the strict watch of almost 700 security guards, making iPhones.

About 30 kilometers (19 miles) away stands another iPhone assembly facility, this one run by Pegatron Corp., now controlled by the Tata Group.

There, about 10,000 people, most of them women, work in an equally disciplined environment.

The development forms part of Apple’s broader effort to build production capacity in India.