Mark, thanks for that explanation. I also think the first re-routing was probably in response to a d/f plot of U-boats detected, but haven't got as far as you with analysing the data. My original reaction to reading the account in 'Nightmare Convoy' was that a U-boat threat must have been detected, as the order to re-route to a more easterly course, closer to the occupied coast (in harms way) could only have been given in the face of a clear and present danger from the west or northwest. Changing the route of convoys at sea was common, in fact it was routine: this was what the Submarine Tracking Room was there for. But the methods used to locate U-boats were secret then and spurious reasons were usually released to account for new orders being given: lack of fuel fits perfectly with this requirement for a cover story despite, as Amanda points out, the story not fitting if you have more detailed knowledge of the ships concerned.

There are at least twenty documents to go through at Kew, and I believe several of these have been released since Lund & Ludlam wrote 'Nightmare Convoy'. I start on them next week, so hopefully I will be able to shed some further light. Many documents are still classified because of their continuing relevance to modern signals intelligence methods.

Perhaps you or Amanda have already viewed those records available at Kew?

Regards,
Bruce