The swastika and number is a werhmacht/Heer (army) waffenampt (weapons office) stamp, a proofmark that it was accepted for military service after being tested. It's a tube carrier/protector with a tube residing inside, unless the tube is gone. The tubes will also likely have a waffenampt, BAL (Luftwaffe), or eagle&swastika with M underneath (Kriegsmarine). The Germans tried to reduce the types of tubes produced during the war and so sets were designed to use the same tube type for every function or only two tube types in the same radio. From what I can tell they were way ahead of the allies in radio gear designed for use below 30MHz, we smoked them in radar. Just after end of the war the allies demanded that troops smash every German military radio they came across, but the order was rescinded after a time. This helps explain why so few sets/parts/tubes remain and go for hi dolla to collectors.
Some info on German ww2 electronics;
http://www.laud.no/ww2/This guy has an impressive collection.