I don't actually remember if he was able to get out with it, or if he was caught, or had problems and needed to be rescued by Danes or something, or what. Now I see these pictures after seeing some of the work of the guys on the psubs list, and it looks pretty homely. But still, pretty elaborate for what it was. The flat sided design of this submersible limits this type of design to extremely shallow depths.
Flat sides have a poor resistance to water pressure.
From the front left. The flat hatch is open, and you can see the snorkel. I remember it had like a red rubber ball in it, which would maybe float up, plug the opening, and prevent water from getting in when the sub went deeper than the snorkel. Possibly reduntant and unnecessary. A shot of the control panel through the open hatch, proving the inventor was German.