The Human Liberty Bell: 25,000 soldiers at Camp Dix, New Jersey in 1918
This was one of the earliest of the photos. Though it is also fairly simple in configuration, it's very impressive how they managed to do the lettering to make it legible.
Let's look at two more...
The Human American Eagle: 12,500 nurses and soldiers at Camp Gordon, Georgia in 1918
This is perhaps our favorite of the collection because it involved so many nurses as well as soldiers. If you zoom in at the white lines, you'll see a bunch of proud nurses!