Boeing PBB-1 Sea Ranger
The largest twin-engined seaplane of WWII.
Designed in 1940 as a patrol bomber, able to operate in the Pacific without the need for airfields, the Boeing 344 first flew in 1942. However even by that time the need for long range bombers able to operate independently from airfields had passed. Boeing's production of B-29's was given higher priority, and so only the prototype was constructed. It continued in USN testing until 1947, being informally nicknamed the "Lone Ranger".