As far as advanced units go, attack transports are one of the most powerful pieces you can buy. I wouldn’t go out of my way to develop them for any nation other than the US, Japan, and to a lesser extent the UK. For only 2 IPP more than a regular transport you get a unit that can drop any of your units off on the first round of combat and you don’t suffer double casualties. That means you can purchase a regular infantry instead of a marine for 1 IPP cheaper as an equal unit thereby lowering the cost of your attack to compensate for the higher cost boat. More importantly, you can attack with artillery, tanks, mechs, or any other ground unit on the first round like in A&A. Huge advantage.
The US would greatly benefit from a heavy Carrier too because it can carry 3 planes across the Pacific for 18 IPP. It would cost you 23 IPP to purchase a fleet carrier and an escort carrier to carry the same amount of planes.
Advanced Submarines are a favourite of mine for the US, Japan, Germany, and ANZAC. They’re harder to kill than regulars subs and they have the same punch as a Destroyer. ANZAC can’t afford a big navy so they are very effective working as hunters against Japanese navy stragglers. Japan really has to think twice about splitting small groups of boats off for amphibious assaults and such. Carriers are especially vulnerable because if you nail one with first strike you may sink their planes if they don’t have a landing spot available. Lend leasing them from the Americans is a great idea because you won’t need to develop the tech with the UK. Two birds one stone.
I really loved your ideas about attack transports and advanced submarines!
Considering that some players may adopt different tech strategies and that lend-lease allows the lending nation to give its advanced units to the receiving nation, in theory, all combinations are possible.
Oh, God! You just pushed me over to striving to get just about everything for everyone! Ha!