The Catalina was originally designed to be a patrol bomber, an aircraft with a long operational range intended to locate and attack enemy transport ships at sea in order to compromise enemy supply lines. With a mind to a potential conflict in the Pacific Ocean, where troops would require resupply over great distances, the US Navy in the 1930s invested millions of dollars in developing long-range flying boats for this purpose. Flying boats had the advantage of not requiring runways to take off and land, in effect having the entire ocean available as its runway. Several different flying boats were adopted by the Navy, but the PBY Catalina was the most widely used and produced.
Although slow and ungainly, Catalinas distinguished themselves in World War II as exceptionally reliable aircraft. Allied armed forces used them successfully in a wide variety of roles that the aircraft was never intended for. They are remembered by many veterans of the war for their role as rescuing aircraft, in which they saved the lives of thousands of aircrew shot down over the Pacific Ocean.