Boeing XPBB Sea Ranger The Boeing XPBB - 1 Sea Ranger ( Boeing 344 ) was a prototype twin - engined flying boat Patrol Bomber built for the United States Navy . The order for this aircraft was cancelled to free production capacity to build the Boeing B - 29 , and only a single prototype was completed . Development . Well before the USA entered World War II , the Navy started a program to develop a long - range flying boat , able to cover the vast expanse of the Pacific Ocean . The Model 344 design offered by Boeing was chosen , and a contract for 57 aircraft was awarded on 29 June 1940 . The designation given to the type was PBB for Patrol Bomber , Boeing , the first aircraft of the PB category built by Boeing for the Navy . Nevertheless Boeing did have important experience in the construction of large flying boats , having produced the successful Boeing 314 airliner . To build the large PBB , Boeing started construction of a new lakeside factory in Renton , Washington , that was owned by the US Navy . However , the prototype was constructed mostly in Seattle , and was moved to Renton only to be completed . To achieve the desired long range , the PBB became a quite large aircraft , with a wing span of 139 feet 8½ inches ( 42 . 59 m ) and a crew of 10 . Despite this size , it was powered by just two Wright R - 3350 Duplex Cyclone radial engines , driving three - bladed Curtiss Electric propellers . It was the largest twin - engined flying boat flown during WWII . For a flying boat , the PBB was aerodynamically clean , with a cantilever wing set high on the fuselage . The planing bottom had a single step , and the non - retractable outrigger floats were attached to streamlined , cantilever struts . The lower hull was divided in seven watertight compartments , and a short upper deck provided seating for the cockpit crew . The wing of the PBB was constructed in a centre section and two outer panels . The centre section carried the engine nacelles and contained the internal bomb bays , as well as fuel and oil tanks . The outer wing panels contained main and auxiliary , integral fuel tanks . The defensive armament of the PBB consisted of five powered turrets equipped with Browning . 50 M2 machine guns . They were installed in the nose , in the tail , on the upper fuselage just aft of the trailing edge of the wing , and in two waist positions on the rear fuselage . Except for the waist guns , the turrets had two guns each . Offensive armament could consist of up to 20 , 000 lb of bombs in internal bomb bays in the wing centre section ( five bays on each side ) or of two Mk . 13 or Mk . 15 torpedo es slung under the wing centre section . The 1710 US gallon auxiliary outer and 1565 US gallon inner fuel tanks were intended to be used only in an overload condition , in which the PBB would use catapult - assisted take off to achieve a theoretical range of 11000 miles ( 17700 km ) . Normal range using the main fuel tanks was 4245 miles ( 6830 km ) . In March 1941 the Navy ' s Bureau of Aeronautics asked the Naval Aircraft Factory for a catapult able to launch a PBB - 1 . The NAF duly prepared a design for a Mark VII catapult that would be able to launch a fifty - ton PBB - 1 at a speed of 130 miles per hour . The catapult would be installed on a lighter , so that the flying boat could be lifted onto it with a large crane or hydraulic jacks . However , in the summer of 1942 , while development of the Mk . VII catapult was still ongoing , the Navy cancelled the project because it considered JATO assistance at take - off more practical . The prototype , designated XPBB - 1 , made its first flight on 9 July 1942 from Lake Washington . The aircraft handled very well and was considered technically successful . However , already in 1942 the PBB programme had been cancelled : The need for a long - range flying boat had been reduced by the ability of land planes such as the Consolidated PB4Y to fly long - range missions over the ocean , and construction of a small number of PBB - 1s would have a negative impact on the production rate of the B - 29 . The Navy allowed the Army to use the Renton factory for the production of B - 29 bombers , in return for the use of another factory in Kansas . The single XPBB - 1 was handed over to US Navy , and was used in trials programmes until 1947 , when it was finally retired . Despite suggestions that more aircraft might be built , perhaps by another factory , it remained the single example of the type , and was accordingly nicknamed " Lone Ranger " .