Hello, first i think there is no point in diving to 40m ( look at GWX manual B15 and B16 appendix), keep periscop depth and don't show your periscop. You don't have to wait at 0kn you can keep a speed of 1-2 knots while approaching the convoy, so you can move out of the escorts path
Also another thing, i may be wrong but... it seems that external camera attracts escorts' attention so stay in your boat, rely on hydrophon and check with your periscop when visual contact is possible to adjust course
Hope it will help you!
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