I had a patrol where I refulled from a Milk cow off the american coast and when I started my next patrol I was being waved off from neutral Vichy France in the Med!!!
I sailed back out throught the squeeze, and survived, and doing it with a IXC sub as well. I took some damage (lost 5 of the six bow torpedo tubes, and down to 63% hull intergrity) but sank 6 ships despite the handicap!