From: Upstate New York USA
I don't think broaching depth is explicitly stated anywhere. However, for game purposes it will be right above periscope depth, which in most cases is -20 meters. If you want to experiment, you can test a specific sub right in the game, just start it at periscope depth and raise it 1 meter at a time until the display switches from Periscope" to Surface."
"It's all according to how your boogaloo situation stands, you understand."
Formerly known as Colonel Mustard, before I got Slitherine Syndrome.