I haven't read all of the previous posts, so at the risk of repeating what other people have said.
DUTCH AND BRITISH SUBS
I'd like to see Dutch and Royal Navy subs, mostly as a matter of national pride, I want to dock at Freemantle while flying the Jolly Roger

. The Dutch and Royal Navy ops in the PTO were vastly different from the USN ops. RN subs tended to operate in shallower coastal waters around the Malaysian coast and around the DEI. However, I wouldn't want to see these at the expense of US subs (even/especially the rubbish types) such as the S boats operating from Manilla.
SPECIAL MISSIONS
Self explanatory really. A few random things chucked in such as rescuing downed airmen or assisting in the evacuation of the Philippines.