The Japanese First Air Fleet, on its voyage from the Kuril Islands in the Hawaii Operation, came across the Soviet freighter Uritsky on 5 December. This was only two days before the intended secret attack on the USA. The vessel was allowed to pass unharmed and she then made no known report of having seen the great mass of warships. It is a curious and unexplained incident.
You can find out more about the Japanese First Air Fleet in the following Osprey book: