The centennial of this holiday passed by nearly two weeks back. In recognition and celebration of the friendship and cooperation between the British and the American peoples, in the U.S. and in Canada December 7th, 1918 was variously proclaimed by governors and mayors as “Britain’s Day”, “Great Britain’s Day” or “British Day”, with keynote ceremonies in New York, Washington and Montreal. King George V, French Prime Minister Clemenceau, President Wilson (who was in France) and many other leaders and personages sent messages of support.
Apparently this was a one-off, as there are no reports of the day being observed in succeeding years. Of course, future events would ensure that Americans would long remember the day for an entirely different reason.
You can read about the observance held in Pittsburgh, PA here.
You can read an Australian account of the occasion here.