To win the Pacific War, the U.S. Navy had to transform itself technically, tactically, and strategically. It had to create a fleet capable of the unprecedented feat of fighting and winning far from home, without existing bases, in the face of an enemy with numerous bases fighting in his own waters. Much of the credit for the transformation should go to the war gaming conducted at the U.S. Naval War College. Conversely, as we face further demands for transformation, the inter-war experience at the War College offers valuable guidance as to what works, and why, and how.The fruits of this transformation are so commonplace now that we may easily forget how radical it was. The U.S. Navy emerged from World War I as a battleship fleet similar to other navies. The British had demonstrated that naval aircraft could be a vital auxiliary to the battleships, but anything more was a distant prospect. The war had demonstrated that an amphibious operation could be mounted in the face of resistance, but not that it would be particularly effective. In 1943–45, carriers were the accepted core of the U.S. fleet, and amphibious operations against enemy shore defenses were routinely conducted. Indeed, without them it would have been impossible to fight World War II.If it seems obvious that any naval officer aware of the march of technology would have developed the massed carriers and the amphibious fleet, the reader might reflect that the two other major navies failed to do so. The Japanese did create a powerful carrier striking force, but they made no real effort to back it up with sufficient reserves to keep it fighting. They developed very little amphibious capability useful in the face of shore defenses: They could not, for example, have assaulted their own fortified islands, let alone Normandy or southern France. The British built carriers, but accepted very small carrier air groups because, until well into World War II, they saw their carriers mainly as support for their battle fleet. Like the Japanese, they did not develop an amphibious capability effective against serious defense. Each of the three navies was staffed by excellent officers, often with the widest possible experience. What set the U.S. Navy apart? War gaming at the U.S. Naval War College at Newport, Rhode Island, seems to have been a large part of the answer.