Dr. Bird dropped his glasses and sat bolt upright.
"What kind of engine trouble?" he demanded sharply.
"Their motors are slowing down for no explainable reason. I can't understand it."
"Are their motors made with sheet steel cylinders or with duralumin engine blocks?"
"Sheet steel."
"The devil! I hadn't foreseen this, although it was bound to happen if my theory was right. Tell them to climb! Climb all they know! Don't let them shut off their motors for any reason, unless they are about to crash. Turn this ship to the north and have the pilot climb—fast!"
A nod from General Merton confirmed the doctor's orders. The line of planes kept on to the west, but the flagplane turned to the north and climbed at a sharp angle, her three motors roaring at full speed. With the aid of binoculars, the two ships in trouble could be picked out, falling gradually behind the line. They were flying so slowly that it seemed inevitable that they would lose flying speed and crash to the ground.
"More speed!" cried the doctor. "We've elevation enough!"
The altimeter stood at eight thousand feet when the pilot leveled out the flagplane and tore at full speed toward the laboring ships. The main fleet was twenty miles to the west.