It looks this theme is not that simple.
There was compressed air and compressed oxygen.
Stiebler (not Steibler) was done before:
"
Oxygen in U-boat - U-boat Officer's Reply"
https://www.subsim.com/radioroom/sho...d.php?t=185993
"
Air supply in H.sie mod – New Options Selector 1.6C"
https://www.subsim.com/radioroom/sho...d.php?t=236848
Greetings.