Why not ask if you need a transport to cross the Tasman sea. Heck, people can swim the English Channel so therefore no transport should be required, right?
Fair dinkum. This has got to be one of the weirdest A&A questions I’ve heard.
Also, You may want to look into getting more gray chips, Japanese Tac Bombers, and the proper battle board to replace the defective one in the Pacific game. contact wizards of the coast, tell them the issue, and they will send you a replacement order free of charge.
Zallomallo is right. Because the sub submerged, it no longer blocks the amphibious assault and cannot kill the transport. There was no reason for the sub to submerge, however, as the planes could no longer hit it. If the sub did not submerge, the transport could retreat, assuming it had somewhere to retreat to (if not, it would be lost).