's machine spluttered little balls of colored
lights and the squadron moved eastward--a great diamond-shaped flock,
filling the air and the earth with a tremulous roar of sound.

They reached their objectives without effective opposition. First, the
junction to the north of Bapaume, then the web of sidings at Achiet
smoked and flamed under the heavy bombardment. Quick splashes of light
where the bombs exploded, great columns of gray smoke mushrooming up to
the sky, then feeble licks of flame growing in intensity of brightness
where the incendiary bombs, taking hold of stores and hutments,
advertised the success of the raid.

The squadron swung for home.

Tam with one eye for his leader and one for the possible dangers on his
flank, was a mere automaton. There was no opportunity for displaying
initiative--he was a cog in the wheel.

Suddenly a new signal glowed from the leading machine and Tam threw a
quick glance left and right and began to climb. The other fighters were
rising steeply, though not at such an angle that they could not see
their leader, who was a little higher than they. Another signal and they
flattened, and Tam saw all that he had guessed.

"Ma guidness!" said Tam, "the sky's stiff wi' 'busses!"

There must have been forty enemy machines between the squadron and home.
So far as Tam could see there were eight separate formations and they
were converging from three points of the compass.

The safety of the squadron depended upon the individual genius of the
fighters. Tam swerved to the right and dipped to the attack, his
machine-guns spraying his nearest opponent. Sutton, ahead of him, was
already engaged, and he guessed that Benson, in his rear, had his hands
full.

Tam's nearest opponent went down sideways, his second funked the
encounter and careered wildly away to his left and immediately lost
position to attack, for when two forces are approaching one another at
eighty miles an hour, failure to seize the psychological moment for
striking your blow leaves you in one minute exactly three miles to the
rear of your opponent. The first shock was over in exactly thirty-five
seconds, and beneath the spot where the squadron had passed seven
machines were diving or circling earthward, the majority of these in
flames.

The second shock came three minutes later and again the squadron
triumphed.

Then Tam, looking down, saw one of the bombing machines turn out of the
line, and at the same time Black