t we thought we were alone. About half an hour after the
_McSmall_ had laid those first 'cans,' however, one of the
quartermasters reported sighting a periscope on the port quarter of the
convoy, about five hundred yards distant, and headed away. We signalled
its presence to the convoy, turned eight points to port, and drove at
full speed for the point where the wake of the moving finger had pinched
out.

"We had received a report that morning to the effect that two submarines
were operating in these waters, and there is just the chance, therefore,
that this was a joint attack. Everything considered, however, we have
been inclined to believe that the Fritz we were now starting to make the
acquaintance of was the same one which the _McSmall_ was still
assiduously hunting some miles off to the westward. It was a mighty
smart piece of 'Pussy-wants-a-corner' work, shifting his position like
that under the circumstances; but it was quite possible if the Fritz
only had the guts for it, and that I think you'll have to admit this
particular one had.

"It's seconds that count in a destroyer attack on a U-boat, and the
captain hadn't lost a tick in jumping into this one. The dissolving 'V'
which the ducked-in periscope had left behind it was still visible in
the smooth water when the _Sherill's_ forefoot slashed into it, and it
was only a few hundred yards beyond that a slow undulant upcoiling of
currents marked, faintly but unmistakably, the under-water progress of
the game we were after. There was no oil-slick, understand, because an
uninjured submarine only leaves that behind--except through
carelessness--when it dives after a spell on the surface running under
engines. Then the exhausts cough up a lot of grease and oil, and a layer
of this, sticking to the stern, leaves a trail that rises for some
little time after submergence, and which almost any kind of a dub who
has been told what to look for can follow.

"The spotting of the surface wake of a deep-down submarine, and the
holding of it after it almost disappears with the slowing down of the
screws that make it, is quite another thing. _That_ takes a man with
more than a keen eye--it takes instinct, mixed with a lot of common
sense. It's a common thing to say of a successful look-out that he has a
'quick nose for submarines.' The expression is used more or less
figuratively, of course; and yet the nose--the sense smell--is by no
means a negligible factor in detecting th