 He later successfully defended the Matanikau River area during the September, 1942 Matanikau action.During the Battle for Henderson Field, he led the 1,200 troops of the 124th Infantry Regiment across the Matanikau and attacked U.S. Marine defenses early on October 26, 1942, but his attack was thrown back with heavy losses to his men, contributing to the overall decisive Japanese defeat in this battle.At the Battle of Mount Austen, the Galloping Horse, and the Sea Horse in January 1943, Oka and the 1st and 3rd Battalions from the 124th unsuccessfully attempted to defend a terrain feature called the Sea Horse from American attacks.