The Coastwatcher organization, run by the Royal Australian Navy, placed observers on islands throughout the Pacific to report Japanese naval and air movements. Operating behind enemy lines, often alone or with a few local scouts, these men (and a few women) lived in jungle hideouts, constantly moving to avoid Japanese patrols.

Their most critical contribution came during the Guadalcanal campaign. Coastwatcher Paul Mason on Bougainville consistently provided advance warning of Japanese air attacks, typically giving Henderson Field defenders one to two hours' notice. Martin Clemens on Guadalcanal itself served as a critical intelligence source for the Marines, his native scouts providing information on Japanese positions and movements.

Admiral William Halsey later said, "The Coastwatchers saved Guadalcanal, and Guadalcanal saved the Pacific." Many coastwatchers were captured and executed. Jacob Vouza, a native scout, was tied to a tree, bayoneted repeatedly, and left for dead by the Japanese—yet survived and crawled to Marine lines to deliver critical intelligence about an impending Japanese attack.