The bombardment diminished in fury as they left the first and second line trenches behind them. It was continued to some extent from an elevation further back, but as Tom knew of this formation, and had crept up still higher, no accident happened to them.
At last the air service boys were fully launched on their night voyage through the upper currents. Tom waited until he considered that it was really safe to change their course. He did not want to betray his movements in case some daring Boche pilot started up in a swift Fokker machine to pursue them.
Once he shut off the engines and volplaned down a thousand feet or more. This was done because it was intensely cold up where they were; and the reasons that had kept them at such a high altitude existed no longer. Then again Tom wished to listen to discover if there was another aircraft near them; and this could be done only when his motor was silent.
"No pursuit, Jack!" he managed to call to his chum before they once more straightened out, and again allowed the motor to send forth its loud hum.
Jack had no chance to make any sort of reply. It did not matter, for he, too, had eagerly listened, and had failed to catch any telltale sound.
