An alternate solution to the Indian Ocean problem – and to the similar “Japan invading Moscow from the east” credibility problem – would be to implement a rule based on the secret military agreement reached between Japan, Germany and Italy on 18 January 1942, by which Germany, Italy and Japan defined their respective zones of military operations. Basically, the rule would restrict each side to its half of the game map, without needing to modify the map itself. The section of the agreement concerning the division of zones of operations said:
The German and Italian armed forces, as well as the Japanese army and navy, will, within the framework of the zones allocated to them hereinafter, carry out the required operations.
1. Japan
a. The waters to the east of approximately 70 degrees east longitude up to the west coast of the American Continent, as well as the continents and islands located in these waters (Australia, Dutch East Indies, New Zealand, etc.).
b. The Continent of Asia, east of approximately 70 degrees east longitude.
2. Germany and Italy
a. The waters to the west of approximately 70 degrees east longitude up to the east coast of the American Continent, as well as the continents and island located in these waters (Africa, Iceland, etc.).
b. The Near East, the Middle East, and Europe west of approximately 70 degrees east longitude.
3. In the Indian Ocean, each side may carry out operations across the above-agreed boundary according to the situation.