Turn around at the beginning of the mission and steam away from the attackers. (direction should be SSW if I recall correctly)
The PT boats AI is not "smart" enough to fire torpedos at you while being behind your ship and it won't overtake you either.
All you have to do is set your deckguns on autofire and tell your AA guns manually to fire at the closest PT.
That way you can sink all of them without having to evade a single torpedo.
Lame, but it works
