In the "German watchmaker newspaper" of 1934 (No. 8 page 86 ff) is a small interesting note to be found about the Junghans J80, namely that „Armbanduhrwerke aber auch als Rohwerke bezw. Schablonen in größeren Mengen an Remontagefirmen geliefert….“. Certainly the J81 has been sold in the same way. Watches where these movements are installed and ultimately sold by companies other than Junghans are not easy to find, as there is no reference to Junghans on the dial, as often on the movement.
Here can be shown an example. The dial adorns exclusively the imprint WASSERDICHT (waterproof).
The snap on steel back lets draw conclusions at least on the manufacturer of the case: Wilhelm Becker from Pforzheim. Whether the company Becker only produced watch cases or sold complete watches I do not know.
If you open the snap on back cover, which is additionally secured with a seal, appears a rather unusual movement holding ring. The spiral fixes the movement slightly elastic in the case.
The movement is only marked with "81". The classic Junghans J or the otherwise existing Junghans star is missing. The movement has probably been bought by another company of Junghans and turned into a case by Wilhelm Becker.
The Junghans J81 was also installed by Junghans itself in a watch that was not quite as self-evident "waterproof" called, but only "insensitive to moisture". Junghans probalby had a lot respect from the ingress of water and the difficulties of protecting the movement and did not lean quite as far out of the window as the unknown supplier of the watch shown. Here is a link to the watch, which is insensitive to moisture: Junghans answer to the Oyster
The case of the watch marked WATERPROOF is equipped with a very long tube. The crown is very large for the small size of the watch (33 mm) and has a cork seal that holds the long tube flush. The case back is only snaped on, but is quite solid and is provided with a seal. So the watch may have at least withstood penetrating water for a short time. I will not test it ...