Enemy Attack on Seaborne Trade.
During the [the week up 24th October] 36 ships (150,091 tons) have been reported sunk. Of these, 17 British (89,199 tons), 3 Norwegian (14,080 tons), 3 Swedish (13,533 tons), 3 Dutch (10,878 tons), 2 Greek (7,408 tons), 1 Estonian (1,186 tons), 1 Belgian (5,186 tons) and 1 Yugo-Slav (5,135 tons) were sunk by submarine. Three British vessels (1,722 tons) were sunk by mine, 1 British (1,595 tons) was sunk by E-Boat and a British trawler (169 tons) was sunk by aircraft.
The U-Boats were particularly successful during this period, U-37 had continued to be active since April. They had ready access to the Atlantic and well co-ordinated tactics were now being used to hunt in Wolfpacks, often in response to sightings by Condor aircraft.
British Naval Intelligence worked hard to follow developments in the U-Boat fleet and now established that Lorient was being used as a U-Boat Base:
The main German U-boat dispositions remain as in the last few weeks. Four or possibly five have been at work in the North-West Approaches and further out, one or two well to the Northward between 580 N. and 600 N. There have been indications of submarines on passage both to and from Lorient, and of one homeward bound via the Norwegian Coast which, after being damaged by air attack, entered the Skagerrak. Since the beginning of October it has been noticeable that there have been few reports of submarines on passage through the North Sea; on the other hand, the use of Lorient as a base has steadily increased.
For some time after the 22nd July, when the first U-Boat arrived in Lorient, the port was only used for short visits, but latterly there has been evidence from photographic reconnaissances of as many as 8 or 9 U-boats in the port, and that these are docked and repaired there. It is thought that, in view of the better repair facilities available in French than in Norwegian ports, this policy will be increasingly pursued in the future, and that Norwegian ports will largely be used as stopping places for submarines homeward bound for Germany after 2 or 3 cruises, to give leave. There is no reason to believe that any. of the submarines in Lorient came there by way of the English Channel, and it is possible that fear of air attack, has made them take the long sea route from Germany.
See TNA CAB /66/13/9