If you're talking about WW2, it's the battle of Stalingrad.
If it's about WW1, it would probably be Verdun.
The correct answer is the Battle of the Coral Sea
Although both sides were winners in certain respects, it was a draw in the end which was a bad thing for Japan. The Japanese army had a tactical victory through the numbers of US troops defeated and ships sunk, the US had a strategic victory because Japan could not prepare for the following battles because of the losses suffered in this one.
