top of this great net are lashed immense blocks of wood for
buoys. Two oil-burning destroyers take the netting, and hanging it
between them as deep down in the water as it will go, are ready to seine
the 'silverfish.' The range of a submarine's periscope is little over a
mile in any sort of sea. Vessels that are belching clouds of smoke may
be picked up at distances of from three to five miles, but no more. In
other words, watchful eyes gazing through binoculars may see a periscope
as far as that periscope sees. The destroyers, bearing their net between
them, then pick up a distant periscope. They chart the submarine's
direction (this may be told by the direction in which the periscope is
cutting the water) and calculate her speed. Then they steam to a point
directly ahead of the submarine, and the lashings are cut away from the
net. While it thus floats in the submarine's path the destroyers speed
away out of eye-shot. In a large majority of cases it is claimed the
submarine runs into that net, or one like it. Results are a probable
disarrangement of her machinery and her balance upset. She may be thrown
over on her back. If she comes up she goes down again for good and all
with a hole shot in her hull; if not, it is just as well, a shell has
been saved.

Submarines occasionally escape by changing their course after the nets
have been set; but there appears to have been no instance of the
destroyers themselves having been picked up by the periscope. This
because they set pretty nearly as low as a submarine, and with their
oil-burning propulsion give forth no telltale cloud of smoke. Other nets
are hung from hollow glass balls, which the periscope cannot pick up
against the sea water. These nets are set in profusion in the English
Channel, the North Sea, or wherever submarines lurk, and they are tended
just as the North River shad fishermen tend their nets. When a
destroyer, making the rounds, sees that a glass ball has disappeared,
there is more than presumptive evidence that something very valuable has
been netted.

Naval Lieutenant Weddingen, of the German submarine U-17, has related
the following experience with the British net system. The U-17 had left
her base early in the morning and had passed into the North Sea, the
boat being under water with periscope awash. "I looked through the
periscope," said Weddingen, "and could see a red buoy behind my boat.
When, ten minutes later, I looked I saw the buoy again, stil