Hi Pat

very nice item. This is so called "Doppelbild-Entfernungs-und Zielkurswinkelschätzer" - double
prism stadimeter, used to range finding and estimating angle on bow.

It was used in pre-war attack-periscopes (probably on type II boats). You can see it as a part of Vesikko
control room periscope:
[www.nortfort.ru]

In war-time U-boats, double-prism range-finder was abandon, and the range was found by graticule only.

So the numbers 2017 or 3017 are most likely serial numbers or so.

See these links:
[www.uboot995.homepage.t-online.de]
[www.uboatnet.de]
[www.subsim.com]

Will look forward for more images.

--
Regards
Maciek


[www.tvre.org]