it's really more sensible to consider usa in wwii as two wars i mean the pacific war and the euro war were fairly distinct.  the pacific war as a resounding american victory against a pretty sophisticated enemy, and aside for a bit of australian involvement and british help, it was primarily an american effort. to this day many of the battles are the largest naval battles in the history of mankind. i could honestly make an argument that the us won the largest naval war in human history. what war remotely compares to the pacific war in terms of scope and breadth as a naval conflict?
United States