This photo, featuring Forest Park Post Master Art Schuler, sorting through the special envelopes used to denote the country of origin in the Air Mail system.
This is the letter sent in the 20th Anniversary of the Air Mail flight from Wilbert Vault Organization.
This 20th anniversary commemorative envelope features Wilbert Haase in front of his Fairchild “24”

In 1919 The Post Office Department, without the support of the Air Force, started mail lights from New York City to Cleveland, establishing the transcontinental Air Mail route.  The flying and ground personnel consisted of civilians hired by the U. Air Mail service which was operated independent of the Post Office under control of the Postmaster General.  A strip of land in Grant Park was established to continue the route from Ohio to Chicago.

The Grant Park hanger was limited by size and inclement weather from the lakefront, so a new site was proposed.  Checkerboard Field, located between Roosevelt and 22nd at First Ave., had the best year-round flying conditions and was selected.  Early in 1920 a hangar and small garage were built.  In May the Checkerboard Air Mail Field was in operation.

By May 15, 1920 the Air Mail Service was extended to Omaha, Nebraska- with Iowa City, Iowa as the halfway refueling stop.  Over the course of the next year, Checkerboard, also called the Maywood Air Mail Field would transition to be the main repair and overhaul center for the entire service.

To commemorate the 20th Anniversary of the first flights of the Air Mail system, Wilbert Haase was selected to fly mail during National Air Mail Week in 1938.  This letter highlights many of his life accomplishments, including work with concrete, vaults and air mail.

Wilbert Haase, grandson of Forest Park founder, Ferdinand Haase, was known as an “Edison type” and applied his creativity to the vault business.  When the Spanish influenza epidemic of 1918 and 1919 hit Chicago, burial vaults were seen as necessary to prevent the spread of the disease to others.  Wilbert had managed the family concrete and cemetery business at Forest Home Cemetery and grew it to the Wilbert Vault Manufacturing Company and American Vault Works.

By 1930 Wilbert Haase, had invented the first water-proof concrete vault in the country.  Wilbert took to the skies to introduce his vaults to potential manufacturers throughout the country.  By 1980there were more than 300 manufacturers and distributors from New York to Texas.   

Wilbert is also featured here in this 1949 photo at Forest Park National Bank:

https://www.forestparkreview.com/Community/Blogs/12-21-2018/Flashback-to-the-Silent-Teller-of-1949/

See more about the American Wilbert Vault building on Troost here.