It shows that successfulness in puncturing can be more easily achived by applying tourniquets in several times and releasing the tourniquets after each cannulation when a less venosity appears.
These battlefield medics used a variety of instruments, like hemostatic tourniquets and arterial surgical clamps to curb blood loss, all while making sure to try and disinfect their tools in hot water before use.
You would pull out your trusty tourniquet, slide it on above the arm, tighten it just above where the injury is, tighten the belt and Velcro it just in place like so.