In retrospects, it seems like a ridicolus idea for Germany to attack American ships during WW1. Surely, they must have understood that this would mean that the United States would join the war, which would mean that Germany would lose. Would it not have been more sensible with a more restricted submarine warfare?
To quote an old soc.history.what-if post of mine:
***
Of course they realized that it would bring America into the war.
But their argument was that this would make no real difference--that the US
was helping the Allies as much as a neutral as she would as a belligerent:
"Ludendorff on December 22 [1916] told the Foreign Office again that formal
American participation in the war would amount to nothing, and on the same
day Holtzendorff brought in an Admiralty report to much the same effect. It
dismissed the danger of American troops by showing how much time was needed
for their training and transport; it calculated that the American supply of
munitions--already at capacity--would be less rather than more available to
Germany's enemies because they would be reserved for America's use...The only
disadvantage conceded by the report was the possible increase in American
loans to the belligerents, but the amount of these was already so tremendous
a factor in the economic strength of the hostile coalition that little
additional danger from that source was to be anticipated. Bethmann had for
some time been yielding to the importunities of the military, and the
conference at Pless on January 9, 1917 sealed his defeat by the decision to
renew unrestricted submarine warfare." Paul Birdsall, "Neutrality and
Economic Pressures 1914-1917" in Carl N. Degler (ed) *Pivotal Interpretations
of American History, Volume II*, p. 201.
https://groups.google.com/d/msg/soc.history.what-if/Vstz0jJ8jns/u-FUk7rdH-4J