Guadalcanal became the site of the first major land offensive against the Japanese in the South Pacific. Upon the American invasion of Guadalcanal, Clemens and his scouts were ordered to join the Marines at Lunga on 13 August. Cooperation between Clemens and the U.S. Marines made him a key operative on the island. Major General Alexander Vandegrift gave Clemens "complete charge of all matters of native administration and of intelligence outside the perimeter". Clemens and his scouts provided the U.S. Marines much assistance with continuous raids on Japanese supplies and radio reports of the enemy's position.