Quickly made re-creation of the iron lung sub, more based on the movie version, built with some added amenities and defenses for campaign play. Comes with slowly draining power reserves, limited oxygen, and poorly engineered systems to give you that horrible feeling that you're about to die. Systems recharge at port, so try not to get lost in the abyss for too long.
Addendum: There is no sonar; you are expected to navigate with the proximity sensor, hopes, and dreams.