How do I say "WWI" out loud?

I know it's written WWI, but when I am speaking should I say "World War One" or "World War First" or "First World War"?

Solution 1:

I've always heard people referring to it either as "World War One" or "the first World War". I guess the second is slightly more "formal".

Solution 2:

Looking for what the Corpus of Contemporary American reports, I get the following data.

Solution 3:

World War II is almost always said "World War Two", so by convention, World War I follows: "World War One".
As an interesting aside, Wikipedia notes:

The terms World War I and First World War both became standard (in the United States and Britain respectively) beginning in about 1940 to 1942; prior to that, it was most commonly called The Great War.