Great pictures, Stoo. Maybe that last one is the footage I had in mind?
Here are some pictures and diagrams of the real U-26 Type IA:
A slightly different version of the black and white photo is also in the 'Complete Making of' book (p.105). The caption reads: 'Ford clings to the specially rigged submarine scope (deleted from the film), while bearded mechanical effects supervisor Kit West watches from the water, and Spielberg stands with a bullhorn.' This photo is a few moments before or after the one Dr Bones put up.
As you all probably already know, the submarine pen used was the genuine German wartime one still at La Rochelle, France, complete with original German graffiti on the walls. The Wurrfler submarine used was owned by a German company, who would only permit it to be used at sea if the waves were less than a metre high, as it was so valuable. I think it was the same sub that was being used to film 'Das Boot'.