The RG12D60 is a German full wave rectifier and designed for military equipment and features a 12.6 Volt heater for mobile equipment. The rectified current is 60 mA maximum and the reservoir capacitor has a maximum value of 32μF.
The two anodes share a common cathode and are mounted at right angles to one another, as well as one being inverted.
The glass carries the word Kriegsmarine - German War Navy - and this dates the exhibit to between 1940 (when the Type was introduced) and 1945.
The thin glass tube envelope is 20 mm in diameter, and including the De6 base pins is 66 mm tall.
Reference: Data-sheet. Type RG12D60 was first introduced in 1940.