Having not been in those northern latitudes Ive not witnessed the effects of twilight . However they were not that far north either.....about 500 miles from Brest (roughly). Ive trained south of Tasmania, in the southern hemisphere, which is roughly similar latitude only south of the equator, and it is dark by 2000 most of the year.
The Swordfish were assisted to the target by the cruiser Sheffield, which was unfortunately the target of the first strike. This occurred as a result of crew inexperience and failing light. The second strike, delivered by the experienced crews off the Ark Royal were again guided onto the target by the shadowing cruisers, then illuminated by flares. There was always an aircraft detailed to drop flares and provide assistance to the remaining aircraft of the squadron by radio direction. I used to believe that ASV might have been used during the Bismarck operation, but I now am doubtful. ASV radar was fitted early in 1941, such that by the latter part of the year, Swordfish were using it to itercept Italians merchant convoys crosssing the ditch . They planned to use it in the Indian Ocean operations, and it was used in Madagascar. RDF was used more or less all the time after 1943 when Swordfish were more or less used exclusively on ASW patrol. An ASV equipped aircraft could not carry torpedoes, but it could carry other stores like flares and I believe 5" rockets.
I dont believe that Swordfish were demonstrably more vulnerable than more modern torpedo aircraft (except the very fast types like the C6 Saiun or the heavily protected TBF), as it wqs frequently airborne when German airborne twin engined fighters were about. What was lacking in the RN were sufficient fighters to protect the strike aircraft. In the early part of the war, airstrikes were seldom provided with any escort, there being insufficient to even provide adequate protection for the carriers themselves.
The RN was as surprised as anybody to find that fleets, and carriers in particular could operate in waters dominated by LBA. They reduced the risks by approaching at high speed by night, hitting the target, and then running like hell to get out of SE fighter rqange at least. The carriers were ffrequently attacked by longer ranged TE aircraft, of all types and nationalities, but in these situations the limited CAPs available were usually able to deal with the threat. There was a momentary lapse of caution in January 1941, which almost cost the RN the illustrious. Formidable was deliberately sent into enemy controlled airspace by day in May 1941, and was heavily damaged as well. I dont believe that the swordfish groups attached to either of those carriers were suffering excessive losses in either of those actions