"A World Ablaze, Its Destiny In The Balance"
The primary source and rule book for GURPS WWII.
An attempt to cover the world's most bloody conflict in an RPG from a myriad of different angles. One could hypothetically play a character from any nation involved in the war.
Not the first WWII RPG, but the most detailed treatment of the subject.
This is in a sense a standalone product; specially tuned version of "GURPS Lite" (GURPS Lite for WWII) is included at the end of the book.