Consolidated PBY Catalina
The Catalina was a maritime patrol bomber whose long range and utility made it very useful in a wide variety of combat roles during the war, and it was produced in greater numbers than any other flying boat. They were used for maritime patrol (it was a Catalina that first spotted the Japanese fleet on its way to Midway), anti-submartrine warfare, search and rescue and night shipping attacks (the famous "Black Cats" of the Pacific). Many are still in use today as aerial firefighters. If it were any more useful, it'd be a DC-3.
Cool stuff for PBY lovers:
Check out the PBY T-shirt in the gift shop!