it comprehended almost every
useful article grown, mined, or manufactured. But the amendment to
international law which acted as new fuel for the flames of war,
which aroused the utmost world-wide indignation, and which finally
dragged the United States into the conflict, was that by which
Germany sought to relieve her submarine commanders of the duty of
visiting and searching a vessel, or of giving its people time to
provide for their safety, before sinking it.

[Illustration: (C) U. & U.

_An Air Battle in Progress._]

The German argument was that the submarine was unknown when the code
of international law then in force was formulated. It was a
peculiarly delicate naval weapon. Its strength lay in its ability to
keep itself concealed while delivering its attack. If exposed on the
surface a shot from a small calibred gun striking in a vital point
would instantly send it to the bottom. If rammed it was lost. Should
a submarine rise to the surface, send an officer aboard a ship it
had halted, and await the result of his search, it would be exposed
all the time to destruction at the hands of enemy vessels coming up
to her aid. Indeed if the merchantman happened to carry one gun a
single shot might put the assailant out of business. Accordingly the
practice grew up among the Germans of launching their torpedoes
without a word of warning at their helpless victim. The wound
inflicted by a torpedo is such that the ship will go down in but a
few minutes carrying with it most of the people aboard. The most
glaring, inexcusable, and criminal instance of this sort of warfare
was the sinking without warning of the great passenger liner,
_Lusitania_, by which more than eleven hundred people were drowned,
one hundred and fourteen of them American citizens.

[Illustration: Photo by U. & U.

_A Curtis Hydroaeroplane._]

Against this policy--or piracy--the United States protested, and
people of this country waxed very weary as month after month through
the years 1915 and 1916 Germany met the protests with polite letters
of evasion and excuse continuing the while the very practice
complained of. But late in January, 1917, her government announced
that there would be no longer any pretence of complying with
international law, but that with the coming month a campaign of
unlimited submarine ruthlessness would be begun and ships sunk
without warning and irrespective of their nationality if they
appeared in certain prohibited zone