Which is the documented first military (officially issued) sidecar?
Which is the last service sidecar?
In 1916 the U.S. Army ordered up some Harleys with sidecars to help track down Pancho Villa in the deserts along the Mexican border, and Bill Harley developed machine-gun mounts for the sidecars. Rider magazine
According to that article the first sidecar was invented between 1893 and 1903; 1916 seems like a plausible date for the first military motorcycle.
"plausible" just means that someone else may find an earlier date.....