[Rainer]

I'm already reading it here, so there is no need to inform uboat.net that you are comparing different numbers. The numbers of shipping losses stated in the Appendix of "The War At Sea" counts losses due to all causes in each theatre, while we on uboat.net only show the ships attacked by German U-boats.

Lets take a closer look on January 1943:
We list 49 ships hit by U-boats, but in fact only 35 merchant ships were sunk by U-boats during that month (subtract the ships that were only damaged, the warships and the small sailing vessels).
15 of these 35 were sunk in the South Atlantic, Caribbean, Freetown area, in the Med or in the Arctic, so 20 merchant ships sunk by U-boats in the North Atlantic during January 1943. Only 9 of these 20 were in a convoy when sunk and 7 alone were from the important tanker convoy TM-1 heading from the Caribbean directly for Gibraltar.

In January 1943 about 270 merchant ships were sent from Canada to the UK in eight HX & SC convoys and the 30+ U-boats trying to intercept them only managed to sink 1 ship in convoy and 5 stragglers while losing 1 U-boat.

Even the Coastal Command wasn't sure about the correct use of the Liberators. Initially they converted all available Liberator Mk.I & Mk.II to VLR, but when the first batches of Mk.IIIA arrived they weren't converted and used to patrol the Bay of Biscay instead. If it was so urgent to get more VLR aircraft, why it still took more than 30 days to convert Liberators to VLR configuration in early 1943?

PS: Roskill is a good source but no longer a definitive one because it was written before the extend of Allied code breaking and its huge impact on the Battle of the Atlantic became known.