If Japan had attacked the Soviet Union in 1941

How would Japan turning north against the Soviet Union in late 1941 change naval strategy?

Japan could threaten Soviet Pacific supply routes and Vladivostok, but would gain fewer naval benefits than from southern expansion while risking a wider political crisis.

A northern war would limit the Imperial Japanese Navy to a narrow set of realistic tasks. Coastal bombardments, carrier strikes and a blockade of Vladivostok could disrupt Soviet Pacific supplies and the Trans-Siberian route. Fighting in the east could also prevent Siberian divisions from moving west against Germany. The Soviet Pacific Fleet offered little decisive prize, while a northern campaign lacked the resources and maritime objectives Japan sought in the south. Holding the Japanese fleet ready could nevertheless deter intervention: the Royal Navy was stretched and American reinforcements would need to cross the Pacific. Britain and the United States would have to decide how to respond before Pearl Harbor, making alliance politics a major uncertainty.