A common house rule I used to play with included many more naval units. We also divided all water territoires into four each. (NW, NE, SE, SW.)
This allowed for more dynamic game play and yes, it did seperate islands in island chains so you could conquer part of an island. =)
Naval units we added were:
Name, cost, attack, defend
Destroyer Escort (DE), 6 IPC, 1, 2
Destroyer Dreadnaught (DD), 8 IPC, 2, 2
Light Cruiser or Cruiser, 10 IPC, 2, 3
Heavy Cruiser, 12 IPC, 3, 3
Escort Carrier, 10 IPC, 0, 0 Carries 1 fighter or two Hellcats
Hellcat, 6 IPC, 2, 3 flight range 2