the event
of an accident this buoy is released and rises at once to the
surface. A flag attached attracts the attention of any craft that
may be in the neighbourhood and makes immediate communication with
those below possible. Arrangements can then be made for raising the
boat or towing her to some point at which salvage is possible. An
instance of the value of this device was given by the disaster to
the German submarine "U-3" which was sunk at Kiel in 1910. Through
the telephone the imprisoned crew notified those at the other end
that they had oxygen enough for forty-eight hours but that the work
of rescue must be completed in that time. A powerful floating
derrick grappled the sunken submarine and lifted its bow above
water. Twenty-seven of the imprisoned crew crept out through the
torpedo tubes. The captain and two lieutenants conceived it their
duty to stay with the ship until she was actually saved. In the
course of the operations one of the ventilators was broken, the
water rushed in and all three were drowned.

In some of the Holland ships of late construction there is an
ingenious, indeed an almost incredible device by which the ship
takes charge of herself if the operators or crew are incapacitated.
It has happened that the shock of a collision has so stunned the men
cooped up in the narrow quarters of a submarine that they are for
quite an appreciable time unable to attend to their duties. Such a
collision would naturally cause the boat to leak and to sink. In
these newer Holland ships an automatic device causes the ship, when
she has sunk to a certain depth, registered of course by automatic
machinery, to start certain apparatus which empties the ballast
tanks and starts the pumps which will empty the interior of the ship
if it has become flooded. The result is that after a few minutes of
this automatic work, whether the crew has sufficiently recovered to
take part in it or not, the boat will rise to the surface.

This extraordinary invention is curiously reminiscent of the fact
chronicled in earlier chapters of this book that the most modern
airplanes are so built that should the aviator become insensible or
incapacitated for his work, if he will but drop the controls, the
machine will adjust itself and make its own landing in safety.
Unaided the airplane drops lightly to earth; unaided the submarine
rises buoyantly to the air.

In recent years there have been developed special ships for the
salvage o