As far as I have read, I only know of one major Imperial German figure who strongly opposed the introduction of unrestricted submarine warfare during the First World War, chancellor von Bethmann-Hollweg. He reportedly stated “Germany is finished” when the practice was reintroduced in 1917. As the title asks, did anyone else feel that this naval strategy would bring about Germany’s defeat?
While more can always be said, I have written up this answer before about the decision to implement unrestricted submarine warfare in both 1915 and 1917.