The RL12T2 is a 1930's/1940's German triode audio output valve. The Wehrmacht was the unified armed forces of Nazi Germany from 1935 to 1945 and the 12.6 volt heater suggests that this valve was designed for mobile use.
The BAL code denotes the place where the valve was tested and accepted. The number 1964 indicates valves made by Telefunken in Berlin. BAL codes suggest Luftwaffe. The grid is circular within a circular anode and has radiating fins above the top mica.
The clue from the BAL code is confirmed by the actual Telefunken logo.
The side pin base with the central threaded brass insert. A knob type handle would screw into the base to facilitate rapid replacement. SeeRV12P2000 for an example.
The thin glass tube envelope is 20 mm in diameter, and 10cluding the base pins is 58 mm tall.