Espiritu Santo, New Hebrides, was selected as the headquarters, Espiritu Santo Naval Base, and the main base for the offensive, codenamed "Operation Watchtower", with the commencement date set for 7 August. At first, the Allied offensive was planned just for Tulagi and the Santa Cruz Islands, omitting Guadalcanal. After Allied reconnaissance discovered the Japanese airfield construction efforts on Guadalcanal, its capture was added to the plan and the Santa Cruz operation was (eventually) dropped. The Japanese were aware, via signals intelligence, of the large-scale movement of Allied forces in the South Pacific area but concluded that the Allies were reinforcing Australia and perhaps Port Moresby in New Guinea.