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 mainly because their aircraft - carriers approached Hawaii unnoticed. This allowed them to launch a sudden air - strike. Japanese land forces did not invade Hawaii before the attack, submarines were part of the attack but not the main element for achieving surprise in terms of approach, and the attack was on Pearl Harbor in Hawaii not the US mainland.

Answer:

Japanese aircraft carriers had approached Hawaii unnoticed.