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 largely because their aircraft - carriers managed to approach Hawaii undetected. This allowed them to launch a sudden air - strike. Japanese land forces did not invade Hawaii unnoticed prior to the attack. Japanese submarines were part of the attack but not the main element for achieving surprise in terms of undetected approach. And it was not about Japanese airplanes flying to the US mainland unnoticed for the Pearl Harbor surprise.

Answer:

Japanese aircraft carriers had approached Hawaii unnoticed.