Walter,
With regard to the Sunderland crash and the number of Navigators and other personnel.
1.The Sunderland could operate for 13-14 hours whilst on patrol and it was not possible to stop the war whilst crewmembers left their positions to stretch their legs etc. Sufficient personnel were carried for each "Trade" to ensure that positions were rotated.
2. No 204 Sqn (Sunderlands) operated out of Iceland. It would have been routine practice to send Personnel posted to that Sqn out by aircraft that were routing through Iceland whilst engaged on other tasks.
3. Just how many more revelations of homicidal mania by or on behalf of HMG are we to be treated to?