Question

Why was the Japanese attack on Pearl Harbor surprising?

Answer 1

There was evidence that it was and indeed was not surprising.

Explanation:

It can be seen as surprising as there was no warning and the USA and Japan were involved in talks to try and avoid war. However, there is evidence suggesting the Americans did know an attack was imminent.

The British had broken the Japanese military codes, but we can't be sure they told the Americans as an attack would certainly bring the USA into the war in the Pacific.

Secondly the American carrier fleet was at sea the day of the attack. Given the pivotal nature of carriers in naval warfare particularly in the Pacific during World War 2, some suggest this indicates the Americans knew an attack was imminent.