Vtg Stencil US No. 51
The Vtg Stencil fonts from astype are based on real world stencils from several countries. The US No. 51 design was derived from authentic stencil plates used by the U.S. Army in the 1950s and 1960s.
If you are interested in the current stencil design of the U.S. Army please have a look at Vtg Stencil US No. 72.