Hi again Gray, I'm not saying you're incorrect that the Observer / Navigator could well have spent the complete flight in the Bomb Aimers position but if so why did the Battle have such a long perspex cockpit? (I note that some versions did not have this elongated cockpit). In fact the chart table and navigators compass is shown in this mid section on your cutaway, which would be unacessable to the Navigator if in the bomb aimers laid down position, so I would think that he only took this poition on a bombing run.

Here's a photo of a third man in the cockpit. Interesting looking up this material. I don't think you'd get me to fly in one for all the money in China.