15 degrees.

This is the actual radio conversation (released by the chief of naval operations) of a US naval ship with Canadian authorities off the coast of Newfoundland in October 1995.

CANADIANS: "Please divert your course 15 degrees to the south to avoid a collision"

AMERICANS: "Recommend YOU divert your course 15 degrees to the north to avoid a collision"

CANADIANS: "Negative. You will have to divert your course 15 degrees to the south to avoid a collision"

AMERICANS: "This is the captain of a US Navy ship. I say again, divert YOUR course"

CANADIANS: "No, I say again, you divert your course"

AMERICANS: "This is the Aircraft Carrier USS LINCOLN, the second largest ship in the United States Atlantic Fleet. We are accompanied with three Destroyers, three Cruisers and numerous support vessels. I DEMAND that you change your course 15 degrees north. I say again, that's one-five degrees north, or counter-measures will be undertaken to ensure the safety of this ship"

CANADIANS: "This is a LIGHTHOUSE. Your call"