It's meant for making two loaves of... french bread!
Unfortunately I couldn't find any information on this pan, except for one happy consumer, who wishes she could find another.
There are french bread pans on the market, but not cast iron. They're also called baguette pans.
Wagner used to make them. There's one listed on ebay for "only" $185. I don't think so!
I just got word that only one Griswold french bread pan is known to exist, and it costs thousands.
I've never made french bread, but there's good information and a recipe here.
The pans are specially shaped for even browning.
I'm pretty sure if I wanted to make french bread, a regular loaf pan would work; It would just be a very short loaf. Then again, I'm a very short person.