What's wrong with the Story?

Captain Frank and some of the boys were exchanging old war stories.
Art Bragg offered one about how his grandfather led a battalion against a German division during World War I. Through brilliant maneuvers he defeated them and captured valuable territory.
After the battle, he was presented with a sword bearing the inscription "To Captain Bragg for Bravery, Daring and Leadership. World War I. From the Men of Battalion 8."
Captain Frank looked at Art and said, "You really don’t expect anyone to believe that yarn, do you?"

What’s wrong with the story?

Click here for Answer

World War I was not called World War I until World War II.