Northrop N-3PB - Design and Development

Design and Development

Following increased international tension surrounding the German annexation of the Sudetenland in 1938, the Norwegian parliament granted extraordinary appropriations to modernize the Norwegian Armed Forces. The Royal Norwegian Navy Air Service (RNNAS) and the Norwegian Army Air Service were prioritized for funds from the NOK 50,000,000 Norwegian Neutrality Fund. The RNNAS' share of the funds were designated to buy 12 Heinkel He 115 torpedo bombers and 24 reconnaissance aircraft, as well as several new naval air stations. The Dornier Do 22, Northrop 8-A, Northrop 2GP and Vultee V-11 GB were considered and proposals retrieved. The commission quickly decided the Vultee V-11 GB was the best aircraft to satisfy both air services' needs. On the part of the Royal Norwegian Air Service, the requirements were for a reconnaissance aircraft with a range of 1,500 km, a top speed of no less than 320 km/h and a payload of a 900 kg torpedo or the equivalent in bombs.

On 30 December 1939, Norway sent a purchasing commission to the United States, consisting of a Royal Norwegian Navy Air Service contingent headed by Cmdr. Kristian Østby, and a Norwegian Army Air Service contingent led by Birger F. Motzfeldt. The goal of the commission was to inspect the Vultee V-11, which was serve as a new common reconnaissance bomber for the two air services. Amongst the requirements the commission hoped to fill was to replace the Royal Norwegian Navy Air Service's M.F.11 biplane patrol aircraft. Once in the US, the commission found that Vultee would not be able to deliver the Vultee V-11 within a reasonable amount of time, and another aircraft had to be found. Motzfeldt quickly found that the Douglas 8A-5N would satisfy the NOAAS' requirements. As the Douglas 8A-5N could not be fitted with floats, Østby had to continue looking for an aircraft suitable for the RNNAS. After visits to many of the aviation companies in February 1940, Østby determined that only one manufacturer had both a design, and available production capacity, Northrop Aircraft Incorporated. The commission ordered 24 floatplanes based on the Model 8-A, renamed the N-3PB, "off the drawing board" (literally, the aircraft being ordered prior to the type having flown) from Northrop on 8 March 1940, at a total cost of NOK 6,550,000 to meet this requirement. Half the amount was paid shortly before the German invasion of Norway on 9 April 1940.

The Model 8-A, the export model of the Northrop Attack Bomber series was never intended to serve as the basis of a floatplane and had to be redesigned to meet the requirements of the Norwegian order. The new N-3PB was the first product of Northrop Aircraft, which had reformed in 1939, and was a low-winged cantilever monoplane fitted with twin floats. First intended for a lower powered engine, the N-3PB was ultimately powered by a Wright Cyclone radial engine, of the same type specified for the Douglas 8A-5N bombers and Curtiss Hawk 75A-8s ordered by Norway at the same time, simplifying the eventual maintenance and operation requirements for the entire Norwegian military aircraft fleets.

With the Norwegian operation requirements drawn up for a coastal reconnaissance floatplane, a series of modifications were requested to the original design. The changes included a redesign of the float structure to accommodate either a torpedo or bomb load carried under the center fuselage to supplement five underwing bomb racks. Additional armament changes led to a combination of six machine guns replacing the four machine gun (two fixed forward, two flexible rear-mounted 7.9 mm)/one cannon (forward facing, fixed 20 mm) arrangement that was in the initial design. Provision for a rear under-fuselage gun was also made. Further equipment requirements including fitting a rear fuselage-mounted camera as well as changes to instrumentation and radio equipment.

Before Northrop could complete any aircraft, Norway was invaded by Germany. The invasion and occupation of Norway necessitated that the armament of the N-3PB, originally to be installed in Norway, had to be changed. Initial specifications listed one Oerlikon 20 mm cannon in each wing, as well as two 7.9 mm Fabrique Nationale machine guns each in both fuselage and rear gunner stations. Owing to the lack of availability of the originally specified armament, Norwegian-manufactured Colt heavy machine guns were substituted with four Colt MG53A .50 cal. machine guns in the wings and two .30 cal. Colt MG40s mounted in dorsal and ventral positions of the gunner's rear cockpit.