Great comments --- thanks to all.
I took Torp's advice and slinked away .... but may go back. Some background: (running stock game --I'm a newb --- will upgrade to TMO/RSRDC at end of career), I finished a patrol in the Celebes and got the OK to patrol elsewhere. Although early in the war, I thought the Bismarck Sea would be interesting, but it's a long journey. I made it to Port Moresby, thinking I could top off fuel there, it being a friendly port. But, no. Barely made it to Brisbane and refit fuel and torpedoes.
I have no mission in Rabaul but it is now March 12th --- it has been a month since I sank a ship! Missed one convoy interception north of the Bismarck Sea and am presently engaged in what appears to be another futile attempt to intercept a radio contact along a similar track, from my patrol area closer to Rabaul, some 280 nm away.
Fuel down to 50%.
Can't bear to return to port with 12 torpedoes so ---- if I miss this convoy, I'll go back to Rabaul.
One note: very surprised not to have run into enemy air anywhere around Rabaul. Surely that changes later in the war....
@ Capt von Trapp: excellent ideas from an obviously-experienced skipper. Didn't know about the shore guns --- that might be a TMO thing. I'm using Mark X torpedoes --- no "fast" setting --- but your idea of leading the destroyer on ambush might be just the thing...
@ donna: lol @ your experience in the harbor during a US air raid. [Edited to add:] My ex-grandfather-in-law (if that makes sense) was a B-25 pilot who raided Rabaul IRL.
@ diopos: aye, Greek-American!
Thank you, friends, I will update my adventure....
Edited to add: While @ periscope depth outside Rabaul, I was watching the destroyer, trying to gauge his routine and decide what to do. Suddenly he turned onto a track directly at me (although still @ 13 knots). Got to within 2000 yards --- it was a Fubuki --- I was scrambling to arrange a down-the-throat shot --- until finally he turned away. That was scary, and that's why I left.