Initial Japanese reconnaissance had indicated a trafficable road to Kokoda. Bullard reports the error in this. While the road was improved for vehicle transport to Sonobo, about halfway from Gona to Wairopi, levies from Rabaul and pack-horses would have to carry supplies the remaining distance to Kokoda and further forward. Meanwhile, allied airpower interfered with the Japanese line-of-communication, particularly at the Kumusi River, making it uncrossable by day. Soldiers advanced from Kokoda carrying 16 days' rations. The advance, from the end of July until Ioribaiwa, in mid September was to last for over forty-five days. Their load included ammunition for the artillery and machine guns as well as of rice per man.