An advance party, under command of Colonel Yokoyama Yosuke of the 15th Independent Engineer Regiment was to consist of the main force of the regiment, the 1st Battalion of the 144th Infantry Regiment, and the 1st Company, 1st Battalion of the 55th Mountain Artillery Regiment. It also included 500 Korean and Formosan labourers and 2,000 native labourers from Rabaul. A naval force based on the 5th Yokosuka Naval Landing Party was to land at the same time as the advance party and commence construction of an airfield at Buna. Japanese planning proceeded on the premise that an overland assault would occur.