The 50- to 60-year-old steel cable probably “weakened until the point where it came down” after decades in a damp, subterranean tunnel, said Phillip Eng, the MBTA general manager.

More than 450 MBTA passengers were evacuated from a Blue Line train in the tunnel under the Boston Harbor due to a signal issue Tuesday afternoon.

Hundreds of passengers aboard the Blue Line were evacuated Tuesday afternoon after a train became stuck beneath the Boston Harbor, between the Maverick and Aquarium stations, officials said. Over the course of about an hour,