The leather crotch strap is worn to support the weight of the side arm when using the holster adapter.
This is normally used as part of the leather belt harness set worn by U.S. military units during World War II.

The M1916 model saw service in 1916, but remained in service well into WWII (Korean War, Vietnam).

In WWII the holster was often adapted to the M1936 webgear system, where it was worn with a canvas “pistol belt” (hence sometimes confusion with M1936 holster).

Paratroopers of the 82nd and 101st Airborne, among others, used these in combination with the M1936 suspenders and drop-leg extensions (so it hung lower when wearing webbing).

This is the WW2 pattern version which is on brown leather.Dit is de WW2-patroonversie die op bruin leer is.