ORIGINAL: Q-Ball
Engineer is right, when you set up your defensive perimeter as Japan, you have to set it up so that there are "Moats" everywhere.
What is a "Moat?" A moat is at least 5 hexes separating your base from the nearest Allied base. 5 hexes is the longest-ranged fighter before the P-38; so, that means until late '42, he can only a) bomb it with unescorted bombers, and b) can only put CAP over the hex from CVs.
Basically, he can't attrite you in an air war over a "Moat", and unless he has CV superiority, can't attempt an invasion. Because he can't escort bombers, you can keep the airbse open, and stack it with enough Bettys to threaten his CV's, even if you somehow lost all your CV's, or they are elsewhere. That is why you need PM: It's a Moat. Otherwise, he can crawl up NG, or at least attrite your airpower, either of which is not good.
So, the moral of the story is: Moats are very tough to scale for the Allies unit the P-38 makes its appearance. This makes PM and by extension NG safe for the empire through most of 1942. This is also why you would occupy Lunga for example, when it doesn't have inherent value. It's important because it's at the edge of a Moat.
About the only place you can't set up Moats is SE Asia.
Excellent points here and much like my own thinking. The more and bigger moats you can create the longer the empire is safe. Even in SE asia you can at least build moats that are 4 or 5 hexes, so that Spitfires can't reach, and P40Es and Hurricanes fly at long range. P-38's are the problem of course, but the Allies only have so many to go around.
