You talk as if the U.S.A. guaranteed the integrity of Ukraine's territorial boundaries. Oh, they did by agreement in 1994 in exchange for removing 3000 nukes? Um, never mind.
Unverified report: ( most likely false)
As we have just unofficial sources in the Naval Forces of Ukraine, to the shores of Sevastopol at full speed are two ships the Navy United States.
According to preliminary information, two destroyers carrier battle groups have already passed the Bosphorus.
http://sevastopolnews.info/2014/03/lenta/sobytiya/069215239/