@moralecheck:
Marines get a special bonus and there is no real use for them outside of the pacific. Admittedly this means the only powers who would buy them are ANZAC, India, Japan and USA but that strikes me as fine (unless island hopping in the Med. Sea is popular in some groups […] Thoughts?
I agree that one of the fun aspects of wargames is to explore alternatives (large or small) to what actually happened historically, but one factor you might want to consider is whether, historically, particular countries actually had Marines or not. That could determine whether a particular country in the game would be allowed to buy Marine units. Historically, the USA had them (the USMC), and Britain had them (the Royal Marines). I can’t recall if Australia or New Zealand had them – that would be something for you to check. I think possibly France had them (“fusilliers marins”), but again I’m not sure.
The tricky one to handle is Japan. In his book “Victory at Sea: World War II in the Pacific”, James Dunnigan devotes a section to the Japanese Special Naval Landing Forces (SNLF), in which he basically argues that they were simply sailors who fought on shore with Army weapons, not true Marines. I won’t run though all his arguments (he presents several), but the critical one from a wargaming point of view (because it affects combat bonuses) is that the SNLF were considered by the Japanese themselves to be less capable fighting forces than the regular Imperial Japanese Army, and that they did not have any special expertise in amphibious assaults. The USMC, by contrast, is highly skilled in (and has a lot of specialized equipment for) amphibious landings, and is regarded as an elite force which is often given very tough assignments (which it usually carries out successfully). So giving US Marines an amphibious landing bonus would indeed reflect their capabilities in that area; giving one to the SNLF, however, would be more debatable.