It should of course get harder when you passed the golden days. Fire from long range is logical when escorts makes it impossible to come close, but you can always try to make sure you are ahed of convoy, lay still at 25 m, let the convoy come over you and get up to periscope depth and fire all your torpedos at your targets. Then dive as deep as you can and try to evade escorts. Hairy, scary, but can work if you are careful.
Good luck
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