It said unrestricted submarine warfare would begin immediately.

VOA: special.2010.10.14

In 1917, Germany announced it was instituting a policy of unrestricted submarine warfare.

CNN: Saturday,

But within six months, Germany's resumption of unrestricted submarine warfare and meddling in Mexico led Wilson to send American troops to fight in Europe -- an enormous departure from the U.S. tradition of avoiding conflicts outside the Western Hemisphere.

CNN: Obama can still build 2nd term legacy