Ah, an excellent and deceptively tricky question! The short answer is yes, every single, genuine silver "war nickel" proudly sports a mint mark. It was their most distinguishing feature, aside from their patriotic, nickel-saving composition.
But, as the title from Gainesville Coins, "1942 Nickel No Mintmark," slyly suggests, there's a bit of a twist. The confusion comes down to the year 1942, which was a year of transition for the five-cent piece.
For the first part of 1942, the U.S. Mint was still producing the standard copper-nickel Jefferson nickels. Following tradition, the coins made in Philadelphia during this time had no mint mark. However, later that year, to conserve nickel for the war effort, the mint switched to a new alloy of copper, silver, and manganese. To identify these new silver-content coins, a large mint mark (P, D, or S) was placed prominently above the dome of Monticello on the reverse. This was the first time the Philadelphia mint ever used a "P" on a coin, making it a rather historic moment.
So, if you find a nickel dated between 1942 and 1945, and it has that large mint mark (P, D, or S) over Monticello, you've got yourself a silver war nickel. If you find a 1942 nickel with no mint mark, it's not a war nickel; it's just one of the old-style copper-nickel coins made before the big switcheroo. Therefore, to be a true war nickel, it absolutely must have its mint mark credentials on display.
