Convoys ONS 20/ON 206

ONS 20 and ON 206 were North Atlantic convoys of the ONS/ON series which ran during the battle of the Atlantic in World War II.
They were the subject of a major U-boat attack in October 1943, the third battle in the "Kriegsmarine"s autumn offensive.
Background.
Despite the losses suffered by "Rossbach" and poor results achieved during its attack on SC 143, and
still believing their new weapons and tactics gave them an advantage, BdU ("Befehlshaber der Unterseeboote" Commander of the Submarines) re-organized the boats then in the North Atlantic into patrol line "Schlieffen" with the intention of intercepting the expected west-bound convoys. These were ONS 20 and ON 206.
Ships involved.
ONS 20 departed Liverpool on 9 October 1943. 
Composed of 52 ships it was bound for Halifax, and was escorted by B-4 escort group, which comprised 6 destroyer escorts led by HMS "Bentinck" (Cdr HR Paramor as Senior Officer Escort).
ON 206 departed Liverpool on 11 October 1943;
Composed of 62 ships, mainly in ballast, it was bound for New York and was escorted by B-6 escort group, comprising 2 destroyers, "Fame" (Cdr RA Currie SOE) and , the frigate , and 3 corvettes.
Also in the vicinity was Escort group B-7, in the role of a support group; it comprised 2 destroyers, "Duncan" (Cdr P Gretton) and , and 4 corvettes.
Group "Schlieffen" comprised a number of U-boats from group "Rossbach", re-inforced by newcomers from bases in France and Germany. It had already come under attack whilst re-fueling by aircraft from USS "Card"; one boat was damaged and forced to retire, and 2 boats ("U-402" and "U-603" ) had been sunk. Another 2 boats had collided, and one of these was also forced to return to base for repair.
At the time of the attack on convoys "Schlieffen" consisted of 14 boats, with a mix of experience and type.
When Allied intelligence learned of the position of "Schlieffen", Western Approaches Command decided to seek battle, increasing the defence by joining the two convoys and their escorts, and sending B-7 as reinforcement.
Action.
On 15 October 1943 the convoys were sighted by "U-844", and group "Schlieffen" was direct to converge on the position.
By evening a number of boats were in position and commenced the attack, which became one of the most calamitous of the entire campaign for the U-boat Arm ("U-Bootwaffe", UBW).
During the night of 15/16 October the U-boats attacked but were repelled; "U-844" was damaged by "Duncan" and "Vanquisher" and driven off.
Later on 16 October "U-844" was attacked and sunk by two Liberators, from RAF 86 and 59 squadrons; one Liberator was shot down, but the crew rescued by the corvette "Pink".
Also on 16th "U-964" was sunk by a Liberator of RAF 86; her survivors were later picked up by "U-231".
Early that day "U-470" was damaged by a Sunderland of RCAF 422 squadron; the Sunderland was also damaged, ditching later near the ships of ONS 20 and its crew rescued by HMS "Drury". Later, "U-470" was attacked again, by 2 Liberators from RAF 120 and another from RAF 59, and sunk; 2 of her crew only were picked up by "Duncan". 
The only success for the "Schlieffen" boats that day was when "U-426" sank the freighter "Essex Lance", which was straggling from ONS 20.
During the night of 16/17 October the attack was renewed, but repelled with no success; 
"U-540" was attacked and damaged by a Liberator of 59 squadron; later that day she was attacked again and sunk by 2 Liberators from RAFs 59 and 120.
Also on 17 October U-841 was sunk by "Byard" of B-4 group.
During the night of 17th/18th the shadower "U-631" was sunk by "Sunflower" of B-7 group. 
At this point the convoys made a drastic alteration in course, in order to shake off any shadowers; this was successful in that BdU received two conflicting reports from U-91 and U-413, leading to Schlieffen being sent in the wrong direction.
After pursuit was shaking off, "Schlieffen" was unable to re-gain contact, and in view of the losses sustained BdU ordered the group to retire.
On 20 October, with no further attack developing, B-7 Group detached from the convoys to join ON 207, which was following; 
ONS 20 was handed over to its Western Local Escort Group on 22 October, and arrived at Halifax without further loss on 26 October 1943.
ON 206 met its Local Escort Group on 24 October and arrived at New York on 27 October 1943.
Conclusion.
BdU regarded this operation as a setback, but remained confident that their new weapons and tactics would achieve success. However the loss of 6 U-boats for the sinking of just one ship was a major defeat for the UbW and seen as a victory for the Allies.
Tables.
Allied ships sunk
Axis submarines destroyed