In addition, can you attack moored fleets in harbor with submarines? If I remember correctly some of the most successful and heavily decorated attacks by German U-boats on large warships were on moored fleets after they carefully infiltrated a harbor.
You are probably thinking about HMS Royal Oak. Yes you can, with the midget submarines. Some of the subs can carry the midgets to or near their targets. I have now 21 midget submarines of 1 is active, guarding Kwajalein. They cant be refueled and are vulnerable, so they are basically one-shot weapons. In my first PBEM I used them once to attack Pearl and they managed to sink DD Sims. Usually they are lost in an attack but its possible for one to get in and out of the target port/harbor to be carried back home by the mothership sub.
March 6, 1942China: a new Ki-21 Sentai starts operating from Canton, and there are lots of bombing sorties today. IJA force on the road to Ankang reaches the Chinese again - attack ordered for tomorrow! Bombardment near Sian goes pretty well without a Japanese loss - I seem to be consuming their supplies, as planned.
Burma: A6M3 debuts as a wing of them sweeps Akyab, but Allied fighters dont fly. IJAAF hits the withdrawing British on the Prome-Akyab road. Imperial guards attacks them but despite all the negative modifiers the defenders had and the casualties they suffered week ago, the odds are only 1:2 and they hold.
Bad luck with the dice I think...
DEI: yesterday the Dutch finally moved their submarines out of Soerabaja's port, so I canceled the bomber raid. However I figured they would fly their fighters in hopes of catching the bombers so I flew the 3rd Ku S' Zeros instead. 9 enemy fighters shot down for 1 Zero(pilot wounded). IJN bombers also hit Darwin again but this time all the ships had left the port. I wonder why.
South Pacific: a small enemy task force with 2 ships appears West of Luganville. Pickets I suppose. Noumea has about 40 enemy ships...
The operation to take Efate begins.
Submarines: A Dutch submarine sinks a tiny converted ASW boat near Singapore. IJN subs attack Noumea en masse but dont achieve anything - just one attack on an escorting destroyer that fails. Near Hawaii, enemy ASW force with 4 Clemsons attack I-17 that is badly hurt and may become the first casualty of the submarine fleet. 11 system damage and 56 flotation.
Ships: CLs Tenryu and Tatsuta begin their conversion to CLAAs at Hong Kong.
SigInt: For the 2nd time theres any use of it, as Sydney's detection level is risen to 2. See the screenshots.