Question

how were the japanese able to surprise the us at pearl harbor?
japanese land forces had invaded hawaii unnoticed
japanese submarines invaded pearl harbor unnoticed
japanese airplanes had flown to the us mainland unnoticed
japanese aircraft carriers had approached hawaii unnoticed

Explanation:

The Japanese were able to surprise the US at Pearl Harbor in part because their aircraft carriers were able to approach Hawaii unnoticed, allowing for a sudden and unexpected air - strike. Japanese land forces did not invade Hawaii prior to the attack. Submarines were used but the key element of surprise was the carrier - based aircraft. And the attack was on Pearl Harbor in Hawaii, not the US mainland.

Answer:

Japanese aircraft carriers had approached Hawaii unnoticed