If you look at the posture of your average sports/nature photographer, or any shooter who has to use a long lens, it becomes apparent that the form factor of SLR cameras has some ergonomic deficiencies.
The Photosniper was a riflestock camera developed by the KGB in the 1950s that would apparently give Ivan's shoulders a break while he squatted on a rooftop across from the Embassy for a few hours. Pulling the trigger snapped a photo, which probably took some mental adjustment on the part of the "shooter."
Good luck finding one these days, though California-based photographer Hin Man was lucky enough to score one--along with the User's Manual, replete with photos of a dashing spy using and cleaning the device.
While finding a Photosniper is difficult (or expensive), DIY'ing up a riflestock camera mount doesn't look too hard. (Good luck toting it around in public though!)
[photo credits: Goblirschrolf/Toolmonger, Count Zero, geocities user Vienna]