Which was a more important instrument in World War 2 the aicraft carrier or the sub?

Answer 1

Without a doubt the aircraft carrier. Until WWII, the battleships ruled the waves. But due to the unique ability to project force in any direction for hundreds of miles, through the use of it's aircraft, the carrier changed the way that warfare was conducted on the high seas. As a force multiplier, the carrier was the ultimate weapon. In comparison, the carrier's airplanes could easily spot a sub that was preparing to engage in a torpedo attack. Many U-boats and Japanese subs were sunk by aircraft. Its not really a question of which is more 'important' - they functioned in two different ways. Aircraft carriers projected power, while submarines disrupted supply lines. Both were critical in the success of the US against the Japanese.