It's been a long time since I went Asiatic, but as I recall it was a photo mission out of Pearl to Osaka Bay - after taking the pics and sinking the ships at Osaka I had a few fish left, headed up to Kobe. And found the jackpot.
http://www.subsim.com/radioroom/showthread.php?t=201622
Been going there ever since even if it's not my patrol area - finish the mission, got two small old freighters and some junks and fishing boats and keep running into nothing but junks and fishing boats, ho-hum. Let's go to Kobe and get some serious tonnage. Shallow water, coastal batteries, antisubmarine patrols all over the place, real challenge to sneak in and out but racking up tonnage is fish in a barrel.
