Hear is what Mike161 advised on the light. He seemed to be very familiar with it. It is in a 12 D configuration currently.
I believe the 12-D cell light you have is a "Code-4" light, that was made by L.A. Screw Products in Pico Rivera California. The switches were stamped "Police Equipment - For Police Use Only." They were a blue color (advertisements said the blue matched the finish of most firearms - I never saw a gun that color!) and D-cell only (2 to 7 cells). They were designed so that if the switch failed (which happened alot), it could be removed and the light could still be used by rotating the head to turn it off or on. You could also (with the proper assemblies) change the number of batteries used. I have a 4-cell version; I can change it into a 3-cell or into a 1-cell light. Different size battery lengths could be bought separately, to make larger lights (hence the 12-cell). You could change the type of light beam you had (spot or flood) by changing the reflector (on the very common Kel-Lite, if you wanted to change the beam, you had to change the entire head assembly).
The Code-4 light was very popular with Los Angeles County Agencies in the late 1970's, as the 3 and 4 cell versions were lighter than the Kel-Lite (which meant they better met department weight requirements). The two major problems with this light were: 1) the switches kept breaking (later redesigned) and 2) the deep knurl on the tubes kept shredding the "sap" pockets most Officers carried their flashlights in (later smoothed). By the time these changes were made, the Mag-lite was introduced which "killed" this light.
L.A. Screw Products also made a similar light for firefighters. I forgot what it was called (not many were made), but it was red in color, had a special "smoke cutter" bulb and was stamped, "Fire Equipment - For Fire Department Use Only." I also heard they made a light for paramedics/ambulance personnel that was silver, but I never saw one.
Hope this was interesting.
Mike