Hello,
The waters near Gibraltar are always a good spot. When I'm there, I usually stay about 40km west of the straight. Just stay submerged and wait for a merchant contact. You should be in a prime position to intercept submerged at slow or 1/3rd. As long as you wait for the destroyers/patrol craft to leave sound range, you should't have any problem, but if something does get too close, you have 1000+ feet of ocean depth to play with...plus you should have enough room to sneak away. I will usually stay 2 to 4 days there...I'm almost always of running out of eels by then

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Happy Hunting,
Voyd
PS: Watch out for aircraft during those dates...haven't had much problem with them in the earlier years.