ETO (European Theater of Operations); PTO (Pacific Theater of Operations); CBI (China, Burma, India Theater of Operations) during WWII.

European Theater of Operations Basically the operations in Italy, France, Germany. The Pacific Theater of Operations refer to the operations in Pacific Ocean and the islands.

In the Pacific Theater of Operations, America and its allies fought the Empire of Japan.

You are thinking of the Pacific Theater or PTO (Pacific Theater of Operations). It is the U.S. versing the Japanese.

The Pacific Theater of Operations in WW2. All of the Pacific & Indian Oceans.