This is the P11 ("Underwater Gun") from Heckler &amp; Koch with a test device attached.
Sokrates junior
CC BY-SA 4.0
<a href="//commons.wikimedia.org/wiki/File:HK_P11_mit_pruefgeraet.jpg" title="File:HK P11 mit pruefgeraet.jpg">File:HK_P11_mit_pruefgeraet.jpg</a>