Human Portrait of Woodrow Wilson: 21,000 soldiers at Camp Sherman, Chillicothe, Ohio in 1918
This is another interesting one, namely because of the care they had to take in not just creating the likeness of President Wilson, but coordinating the various levels of whites, grays, and blacks to ensure proper shading and contours.
So how on earth did they figure out how many men to put where?! The entire genius behind these photos came when the photographer realized that by simply the perfect outline on the actual lens of his camera, he could then dispatch men to set up small flags to match the outline. From there, white tape was laid to give the initial outlines.
While this sounds simple enough, can you imagine standing on an 80-foot tall tower and asking a soldier 1000 feet away to "a little to the left...no now to the right...". This is why this is all so impressive. Let's look at a few more examples.
Human US Shield: 30,000 soldiers at Camp Custer, Battle Creek Michigan in 1918
This was their largest photo by number of people involved, but also one of the simplest in terms of configuration. According to historical accounts, the most difficult part was ensuring that not only were the stars all the exact same size, but that they maintained perfect lines and points.