All at once there sounded a loud crash not far below the young air pilots, and a puff of white smoke told where a shrapnel shell had burst.
"Frank, they're firing at us!" exclaimed Billy, who had made an involuntary ducking movement with his head as the sharp discharge burst upon his ears.
Even as he spoke another, and still a third crash told that the Germans had determined the time was at hand to try their anti-aëroplane guns on the strange seaplane that was soaring above the camps.
"That means we'll have to climb higher, so that their guns can't reach!" Frank immediately decided.
It was indeed getting rather warm around them, Billy thought. The shrapnel puffs seemed to be above, below, and on every side, and it was a wonder that neither of them received a wound.
"Only for the speed we're hitting up, the story might be a whole lot different, according to my notion, Frank. They have a hard job to get our range, you see."
"Yes, most of it bursts back of us, showing a faulty figuring," the pilot explained, as he started a corkscrew movement of the seaplane calculated to cause the aircraft to bore upward in spirals.
The guns, far below, kept up a merry chorus. Billy could hear the faint noise made by the continuous discharges, and the puffs of smoke that seemed to rise in a score of places at the same time told him how eagerly the German gunners were trying to strike that elevated mark.
Now the shrapnel ceased to worry Billy, for he saw that none of it seemed to be bursting around them as before. The limits or range of the anti-aircraft guns had apparently been reached.
"We're safe from the iron rain up at this height, Frank. What does the barometer say?" he asked, with that spirit of curiosity that had made him a good reporter in the old days.
"That's too bad," replied Frank, as he bent forward to look.
"Don't tell me that the only fragment of a shell that's struck home ruined our fine barometer!" cried Billy.
"Just what happened," he was told. "At any rate, it's knocked to flinders; and I think I must have had a pretty close shave. But we can buy a new one when we get back to Dunkirk. As near as I can give a rough guess we must be between three and four thousand feet high."