Way back when the FAA was born and required tail numbers on aircraft, Northwest had the opportunity to have all their tail numbers end in NW. They decided to pick US as the suffix for all of our tail numbers. This was decades before there was a USAirways.

When they ran into duplication problems, we had to put NW as the suffix to a very small portion of our fleet. But nearly every NWA aircraft has the tail suffix of US.

Carl