What Did U.S. Postal Service Planes Look Like During World War I?

What an awesome old photo of a U.S. Postal Service plane from 1918.

Two Curtiss JN-4H "Jenny" airmail planes parked at the temporary airmail field at Washington, DC’s Polo Field, a small strip of grassy land between the Tidal Basin and Potomac River.
Two Curtiss JN-4H “Jenny” airmail planes parked at the temporary airmail field at Washington, DC’s Polo Field, a small strip of grassy land between the Tidal Basin and Potomac River.

Source: Smithsonian