If you have the reinforced titanium aft torpedo tube that can operate at extreme depths as was fitted on U-571, also seen in the movie (endorsed by a learned rear admiral of the navy) it is now time to sacrifice Bernard and shove him in there along with some other trash (rotten foodstuff, dead bilge rats, etc.) and fire the tube!
The filth after it reaches the surface will fool the enemy hunters into thinking that you've bought the farm and they'll leave in a moment after giving you laps of honour. That is assuming that they're not already familiar with the trick.
Problem solved!
Or on a serious note, if you manage to lose the destroyers, which is going to be difficult because the strait is narrow and very heavily patrolled as it is, move near the african coast and travel submerged (periscope depth) preferably at a silent running speed not going above 3 knots normally except for maneuvering your boat into a position that is safe from any incomming patroller that might detect you. The elco torpedo boats are too fast for a surfaced transit through the strait and they will mostly detect you before you can submerge.