From December 18 – 24, 1941, nine Japanese submarines positioned along the American West Coast attacked eight merchant ships. Two ships were sunk, two damaged and six seamen were killed. A plan for all nine submarines to shell selected U.S. coastal cities on Christmas Eve was canceled at the last minute.
Unlike the subsequent German U-Boat campaign off the East Coast, this was the only time during the entire war that more than one Japanese submarine at a time appeared off the West Coast.
On December 24, 1941 a B-25, flying in poor visibility out of McChord Army Air Field, reported an attack against a Japanese submarine off the mouth of the Columbia River. Further investigation failed to verify the report. Early anti-submarine warfare efforts by the USAAF were hampered by lack of experience, training and equipment. Targets perceived as submarines were often derelict vessels, trees or whales.
Here is an excellent reference on Imperial Japanese submarines.
My historical fiction novel Enemy in the Mirror: Love and Fury in the Pacific War follows the exploits of a junior officer on the Imperial Japanese Navy submarine イ-25
Love that book!