Chinese laborers pull a heavy concrete roller at an American base in China during WWII: "All the runways in China were made of crushed stone. They started the base with the larger stone and each layer that was added was of a smaller stone. The final layer of the runway surface was was made of finely crushed stone that was rolled and rerolled by Chinese coolies pulling a huge stone roller as shown in this picture. One of the big problems with our runways was the larger stone kept working their way to the surface and the runways had to be constantly policed to remove these sharp stones to eliminate tires from blowing out on landings and take-offs." Caption courtesy of Elmer Bukey.