Ummm you don't have to sink everything you come across.
I just ran my first mission with TM 1.6 and made it from Pearl to Honshu and then the China Sea and back to Pearl and only fired two torpedos. The sinking mechanics are great! I sat there idle for the better part of an hour waiting for the ship to finally give it up and sink.
Most of the time was spent motoring from point A to point B in open ocean, then evading aircraft once I got near enough to their bases.
All in all! I apprecaite all the work done by those whose work was incorporated into TM!
This was by far one of my better missions even though I only sunk one ship.