Saigo was appointed the Satsuma group's Sashihiki commander of the Tokaido spearhead army on February 12th, and he was appointed the Shimo-sanbo staff of Tosei-daitokufu (Kuge was the appointed staff officer, the office of shimo-sanbo was the actual staff officer), then left first with the spearhead army (Hanjiro NAKAMURA, who was the Ichiban-shotai Taicho (commander of the first platoon), Shinpachi MURATA, who was the Niban-shotai Taicho (commander of the second platoon), and Kunimoto SHINOHARA, who was the Sanban-shotai Taicho (commander of the third platoon), and they occupied an important part of the Hakone Town of Tokaido.
西郷は2月12日に東海道先鋒軍の薩摩諸隊差引（司令官）、14日に東征大総督府下参謀（参謀は公家が任命され、下参謀が実質上の参謀）に任じられると、独断で先鋒軍（薩軍一番小隊隊長中村半次郎・二番小隊隊長村田新八・三番小隊隊長篠原国幹らが中心）を率いて先発し、2月28日には東海道の要衝箱根町を占領した。