The PBY Catalina became the most widely used flying boat, and the largest Navy aircraft. With a carefully streamlined look, the "catalina," named by the Navy in 1941, was 100 feet long and all metal. It was principally designed for long-distance flights over water---having a range long enough to fly directly to Hawaii, Alaska, and Panama. Its maritime roles included patrolling, anti-submarine, anti-ship, and search and rescue.
Anticipating potential conflct in the Pacific Ocean, funding for developing long-range flying boats was started under a mass invitation by the U.S. Navy calling big manufacturers to submit design entries. It was Consolidated's design that ultimately beat Douglas's more conventional XP3D-1 model. The PBY Catalina had retractable, out-board floats that became wing tips, and its wing contained essential fuel tanks. A design probelm did persist, however. The Catalina was plagued with directional stability well into WWII. Despite that, by 1935 it had proven itself by breaking a long-distance flying record as a seaplane.
During WWII, the Catalina was the principally Allied patrol seaplance and was used in a variety of ways---most notably for over-water rescues of airmen, and even in locating the Bismarck.It was also involved in combat against U-boats and submarines. After the war, the Catalina was used in the commercial sector mostly---freight and passenger transport, and efficient firefighting. Some still fly today, even long-distance trips, a sure testament to the classic aircraft's design.