The U.S. Postal Service celebrated 100 years of airmail on Monday.

It's been a century since the first U.S. government airmail plane took flight in May of 1918. To mark the occasion, pilots are flying vintage planes retracing the west coast route, with a stop at Meadows Field in Bakersfield on Monday.

The planes used during the flight are Stearman Speedmail Biplanes, made popular in the 1930s.