T H E A R M Y A I R F O R C E S I N W O R L D W A R I 1
important tactical conclusions. For example, they determined that
the probability of a successful attack on a long-submerged submarine
was extremely small. Conversely, only U-boats which could be at-
tacked while on the surface or within, a t most, thirty seconds after
submerging offered profitable targets, a fact which encouraged the
use of depth bombs set for detonation at relatively shallow depths,
say twenty-five to thirty feet. British experience also indicated that,
to insure a successful attack, one of the bombs dropped must explode
within little more than a dozen feet of the U-boat’s hull3’
Such items of tactical information the American units welcomed
and found very valuable. But much of the job of hunting U-boats had
necessarily to be learned by doing. Consequently, during these early
months of the campaign, each AAF unit operated for tactical pur-
poses in large part as its commander saw fit; and the data on each
attack were eagerly studied in I Bomber Command headquarters with
a view to the evolution of a tactical doctrine of its own. Many of
the lessons were elementary. It was found to be well, for instance,
not to pay too much attention to the appearance of oil slicks on the
surface of the water, as they did not indicate necessarily the presence
of a submarine. From the air, too, it was easy to mistake the wake
left by the fin of a shark for that produced by the periscope of a sub-
marine, a fact from which the larger forms of marine life may on more
than one occasion have
Many other lessons involved increasingly subtle understanding of
the conditions under which attacks might be undertaken with the
greatest chance of success-the use, for example, of cloud cover as a
means of concealment and surprise in daytime attacks, and an ap-
proach toward the target down the moon path by night. If a sub-
marine submerged before an attack could be delivered, it was found
to be advisable for the attacking plane to use “baiting” tactics, which
involved leaving the area for a good interval and then returning to
it in the hope that the enemy might in the meantime have surfaced
and be thus open to another attack. In many other respects the learn-
ing process was far from complete by July of 1942. Opinion still dif-
fered as to the advisability of dropping an entire bomb load on the
initial contact; and it was still debated whether it was better to attack
the U-boat from the side or along its longitudinal axis. But the data
was beginning to arrive in quantity sufficient soon to remove such
questions from the realm of opinion. Finally, the development of
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