To the left of the medical tent, go through the gap to the water tower, then look for this item on the far left by the wall - it's partly obscured by the horse in the foreground.
"The war effort suddenly required a larger medical corps and there were not enough qualified personnel. So manuals were published and distributed to help volunteers train.
The manuals provided a whole host of practical solutions to logistical and
medical problems at the front, such as how to make a splint or stretcher
using rifles and their straps."