Initially long range naval patrol flying boats were used in the effort, and later in the war during the struggle to improve air coverage over the commercially important sea lanes (SLOC), air strips were built to support land based aircraft which supplied, augmented and complemented the PBY Catalina patrol planes in the vitally important ASW mission. The United States and Great Britain still jointly operate the airfield on Ascension Island, which also serves as a space-based communications and navigation nexus and hub (Ground station). One of only five Global Positioning Satellite (GPS) system ground stations is located there.