Catalinas established numerous long-distance flight records during the prewar years and even before the United States entered World War II played a pivotal role in combat operations. In May 1941, a Lend-Lease PBY flown by Ensign Leonard Smith, a naval aviator serving as an observer with the British Royal Air Force, located the German pocket-battleship Bismarck, enabling the Royal Navy to close in and sink her. When the Japanese attacked Pearl Harbor on 7 December 1941, a PBY that made the only aerial attack against the Japanese, bombing a midget submarine. During the pivotal Battle of Midway in June 1942, PBYs spotted the Japanese invasion and carrier strike forces.

During World War II Catalinas performed a variety of essential duties, including long-range scouting and anti-submarine patrols, convoy escorts, search and rescue and bombing operations. It was in the latter functions that the PBY established its greatest legacy, equipping so-called Black Cat squadrons that carried out effective night attacks against Japanese shipping and installations. Two other PBY squadrons were equipped with magnetic anomaly detection gear in order to locate submerged submarines. Retro-bombs were also installed which, when fired backwards at a velocity equal to the speed of the aircraft, dropped straight down upon a target.

The last of the Navy's PBYs were retired in 1957. However, many of the aircraft are still in active use today, including service in fighting forest fires. The aircraft lands on lakes and scoops up water in special internal tanks for release on hot spots.