The legendary "Medi Nixe" from (Medi)medical industries Leipzig. The first and only industrially produced in the GDR oxygen rebreather for sports divers.
It was produced from about 1954 - 1959/60 . Then stop the production was because of alleged dangers of oxygen diving, but rather because of the potential "escape risk" .
Many thanks to Dieter Florian,dive shop on dive base at the lake "Kulki", a>, he demonstrates me this fantastic device.