Roberts and his battalion then reinforced Midway, Johnston and Palmyra atoll garrisons and was promoted to the temporary rank of lieutenant colonel on May 8, 1942. He ultimately embarked for Guadalcanal, Solomon Islands and took part in the Landing at Tulagi on August 7, 1942. The 3rd Defense Battalion successfully hit three enemy ships that had beached themselves to land troops and repulsed 133 bombing attacks by Japanese planes. Roberts then took part in Battle for Henderson Field at the end of October 1942 and his battalion defended Lunga Point against an enemy counterattack from the sea. He was promoted to temporary colonel on October 30, 1942.