"And the hull. How thick is it?"
He chuckled without humor.
"If you hit it with a city block at a thousand miles an hour, it might break."
She was figuring with a pen-stick on the smooth surface of the control board.
"How far are we into the tunnel?"
He consulted the mileage chart.
"Half way. It's...."
"Good," she said. "Turn on the blades. Use all the power you have."
There was an undercurrent of fear in her voice. He was sure that she struggled with herself at this moment to keep from breaking down. When she spoke again, the howl of the rotating blades drowned all other sound. Without stone or metal to work on, the blades were screaming at top speed, cooled only by the oil. The Z1000 was a strange, rumbling giant, stumbling ahead in the darkness.
"Blair," Sheila Graham said quietly, "Are you afraid to die?"