well i've never been Japanese, but i'm pert' sure you must own the base, if you want to unload units from TranTFs.
so if 21div doesn't have enough oomph to capture the hex in a day or 2, you must rtb w/ your TranTF, unload, then reload for Amph. choose this point carefully, it must be close, w/ available fuel, w/ NavSupp, w/ air-cover, etc.
dunno what the state of 21div is now, but since this is Jan42, enemy morale is gonna be low, & the defenders could be v. brittle. if 21div has supply, you can either continue to attack in hopes of a quick capture, or switch to defense & try to hold out until the 2nd echelon is re-organized.
look on the bright side, sounds like you got some hits on enemy CVs! enemy base forts will be low, so keep hitting w/ LBA.