SCR 717C was the tub-like potrusion hanging below the trailing edge of the main wing on C-47s. It was intended for Pathfinder (C-47s) and Serial leader aircraft. It is obvious on this less than famous photo of 42-92717...about 3/4 down this thread...
http://www.warbirdinformationexchange.o ... p?p=483884. 8Y+S
The tub covers a small radar dish. The display could be generated in two ways. If it was interrogating BUPS it would appear as a blip on a CRT screen in the nav compartment. Alternately, the CRT could display a very crude "coastline" black and white display of shorelines of lakes and rivers or coastlines. I could not "see" roads and cities. But could see a river snaking through a town or city. With reference to a map the navigator could make a positive ID on location. Or if he was doing a righteous DR or time and distance run he could anticipate a particular water feature to get a location.
Field Orders for D-Day stated that planes carrying SCR-717C would not carry wing or fuselage bundles.
C-47s were pulled from the line in small groups of 3 to 5 sequential tail numbers to be fitted with 717C. All passed through the IX TCC Pathfinder School (Prov) before assignment to a TCC Group.
Lead crews were usually trained by the Pathfinder School. Exceptional individuals were "retained" by the Pathfinder School as it was an operation unit tasked with both training and combat missions, and since Groups would not send these individuals if asked, the Pathfinder School just kept them as they passed thru the School.
15159 (re-numbered) (Argonia) on display at Ste Mere Eglise Airborne Museum sports an undersized tub and is a poor representation. 096 at the WW2 Museum in New Orleans has yet to be fitted with a 717C tub.
I have a page out of the 717 manual showing the dish array in the tub as well as either A or B mounted in a B-24 for ASW.
When I find that page I will add to this thread.

