It is a great information, I always believed the Deltrintem were only civilian binoculars.
But what you report, the fact Erfle worked early on this device is a mystery.
He was at the head of the telescope department in 1918 and worked for submarines optics.
Another fact to consider : Germany was very poor after 1918 till 1930, pressed they were due to the Versailles treaty. They were costly products for common people.
Perhaps at start, the fact that Erfle equiped them with his lenses probably means they were used as military devices on submarines U35 during ww1 as an officer light spotting/survey bino.
The 5 lens is the classic wide field EP, not center sharp. The 6 lens may be sharp in center. (not a Kaspereit I believe)
Then why such a model could'nt go to the public market after war as a surplus ?
It is interesting to search in this book about an initial a waterproof military version, could be a nice historic discovery.