I just finished do this, although I only had to go as far as Yokohama.
This is in RFB mod...
I went in on the surface at night, standard speed... Didnt see any patrol ships on the way in. Took my pictures, then went and sank an Akagi(sp?) heavy cruiser... which I guess alerted the defenses.
Getting out was harder, I ran at flank on the surface but had to dive to avoid a DD. thankfully I had just enough room under my keel by then to evade the him.
I was a little suprised it was so easy, that was my first patrol, Dec 41.
Of coarse after that things took a turn for the worse, came across a convoy, sunk one ship, missed my other shot and was then pounded by 3 DD's, one of which blew my the tip of my bow off... No major flooding though.