Keith was called to active duty on February 20, 1941, and served "stateside" until his unit was transferred to the South Pacific in the spring of 1942 during the build up for the first Allied offensive in that theater — the Battle of Guadalcanal. He was with the first unit to land on Guadalcanal for the battle, initially serving on the staff of the commander of the landing party, then being assigned to the assault forces of the ground combat element. He landed with the Marines at Tulagi on Solomon Islands on August 7, 1942 during the Battle of Tulagi toward the end of the Japanese Tulagi campaign. His unit then became part of the invasion force of the Guadalcanal campaign.