World War II: Northrop P-61 Black Widow

In 1940, with World War II raging, the Royal Air Force began seeking designs for a new night fighter to combat German raids on London. Having used radar to aid in winning the Battle of Britain, the British sought to incorporate smaller airborne intercept radar units into the new design. To this end, the RAF instructed the British Purchasing Commission in the US to evaluate American aircraft designs. Key among the desired traits was the ability to loiter for around eight hours, carry the new radar system, and mount multiple gun turrets.

During this period, Lieutenant General Delos C. Emmons, the US Air Officer in London, was briefed on British progress relating to the development of airborne intercept radar units. He also gained an understanding of the RAF's requirements for a new night fighter. Composing a report, he stated that he believed the American aviation industry could produce the desired design. In the United States, Jack Northrop learned of the British requirements and began contemplating a large, twin-engine design. His efforts received a boost later that year when a US Army Air Corps board chaired by Emmons issued a request for a night fighter based on the British specifications. These were further refined by the Air Technical Service Command at Wright Field, OH.

Specifications

General

• Length: 49 ft., 7 in.
• Wingspan: 66 ft.
• Height: 14 ft., 8 in.
• Wing Area: 662.36 sq. ft.
• Empty Weight: 23,450 lbs.
• Loaded Weight: 29,700 lbs.
• Maximum Takeoff Weight: 36,200 lbs.
• Crew: 2-3

Performance

• Maximum Speed: 366 mph
• Range: 610 miles
• Rate of Climb: 2,540 ft./min.
• Service Ceiling: 33,100 ft.
• Power Plant: 2 × Pratt & Whitney R-2800-65W Double Wasp radial engines, 2,250 hp each

Armament

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• 4 × 20 mm Hispano M2 cannon in the ventral fuselage
• 4 × .50 in M2 Browning machine guns in the remotely operated, full-traversing upper turret
• 4 × bombs of up to 1,600 lb. each or 6 × 5 in. HVAR unguided rockets

Northrop Responds

In late October 1940, Northrop's chief of research, Vladimir H. Pavlecka, was contacted by ATSC's Colonel Laurence C. Craigie who verbally detailed the type of aircraft they were seeking. Taking his notes to Northrop, the two men concluded that the new request from the USAAC was nearly identical to that from the RAF. As a result, Northrop produced the work done earlier in response to the British request and immediately had a head start over his competitors. Northrop's initial design saw the company create an aircraft featuring a central fuselage suspended between two engine nacelles and tail booms. The armament was arranged in two turrets, one in the nose and one in the tail.

Carrying a crew of three (pilot, gunner, and radar operator), the design proved unusually large for a fighter. This was necessary to accommodate the weight of the airborne intercept radar unit and the need for extended flight time. Presenting the design to the USAAC on November 8, it was approved over the Douglas XA-26A. Refining the layout, Northrop quickly shifted the turret locations to the top and bottom of the fuselage.

Subsequent discussions with the USAAC led to a request for increased firepower. As a result, the lower turret was abandoned in favor of four 20 mm cannon mounted in the wings. These were later repositioned to the underside of the aircraft, similar to the German Heinkel He 219, which freed up space in the wings for additional fuel while also improving the wings' airfoil. The USAAC also requested the installation of flame arrestors on the engine exhausts, a rearrangement of radio equipment, and hardpoints for drop tanks.

The Design Evolves

The basic design was approved by the USAAC and a contract issued for prototypes on January 10, 1941. Designated the XP-61, the aircraft was to be powered by two Pratt & Whitney R2800-10 Double Wasp engines turning Curtiss C5424-A10 four-bladed, automatic, full-feathering propellers. As the construction of the prototype moved forward, it quickly fell victim to a number of delays. These included difficulty obtaining the new propellers as well as equipment for the upper turret. In the latter case, other aircraft such as the B-17 Flying Fortress, B-24 Liberator, and B-29 Superfortress took priority in receiving turrets. The problems were eventually overcome and the prototype first flew on May 26, 1942.

As the design evolved, the P-61's engines were changed to two Pratt & Whitney R-2800-25S Double Wasp engines featuring two-stage, two-speed mechanical superchargers. Additionally, larger wider span flaps were used which permitted a lower landing speed. The crew was housed in the central fuselage (or gondola) with the airborne intercept radar dish mounted within a rounded nose in front of the cockpit. The rear of the central fuselage was enclosed with a plexiglass cone while the forward section featured a stepped, greenhouse-style canopy for the pilot and gunner. 

In the final design, the pilot and gunner were situated toward the front of the aircraft while the radar operator occupied an isolated space towards the rear. Here they operated an SCR-720 radar set which was used to direct the pilot towards enemy aircraft. As the P-61 closed on an enemy aircraft, the pilot could view a smaller radar scope mounted in the cockpit. The aircraft's upper turret was operated remotely and targeting aided by a General Electric GE2CFR12A3 gyroscopic fire control computer. Mounting four .50 cal. machine guns, it could be fired by the gunner, radar operator, or pilot. In the last case, the turret would be locked in a forward-firing position. Ready for service in early 1944, the P-61 Black Widow became the US Army Air Forces' first purpose-designed night fighter.

Operational History

The first unit to receive the P-61 was the 348th Night Fighter Squadron based in Florida. A training unit, the 348th prepared crews for deployment to Europe. Additional training facilities were also used in California. While night fighter squadrons overseas transitioned to the P-61 from other aircraft, such as the Douglas P-70 and British Bristol Beaufighter, many Black Widow units were formed from scratch in the United States. In February 1944, the first P-61 squadrons, the 422nd and 425th, shipped out for Britain. Arriving, they found that the USAAF leadership, including Lieutenant General Carl Spaatz, was concerned that the P-61 lacked the speed to engage the latest German fighters. Instead, Spaatz directed that the squadrons were equipped with British De Havilland Mosquitoes.

Over Europe

This was resisted by the RAF which wished to retain all available Mosquitoes. As a result, a competition was held between the two aircraft to determine the P-61's capabilities. This resulted in a victory for the Black Widow, though many senior USAAF officers remained skeptical and others believed the RAF had deliberately thrown the contest. Receiving their aircraft in June, the 422nd began missions over Britain the following month. These aircraft were unique in that they had been shipped without their upper turrets. As a result, the squadron's gunners were reassigned to P-70 units. On July 16, Lieutenant Herman Ernst scored the P-61's first kill when he downed a V-1 flying bomb.

Moving across the Channel later in the summer, P-61 units began to engage manned German opposition and posted an admirable success rate. Though some aircraft were lost to accidents and ground fire, none were downed by German aircraft. That December, the P-61 found a new role as it helped defend Bastogne during the Battle of the Bulge. Using its powerful complement of 20 mm cannon, the aircraft attacked German vehicles and supply lines as it aided the besieged town's defenders. As the spring of 1945 progressed, P-61 units found enemy aircraft increasingly scarce and kill numbers dropped accordingly. Though the type was also used in the Mediterranean Theater, units there often received them too late in the conflict to see meaningful results.

In the Pacific

In June 1944, the first P-61s reached the Pacific and joined the 6th Night Fighter Squadron on Guadalcanal. The Black Widow's first Japanese victim was a Mitsubishi G4M "Betty" which was downed on June 30. Additional P-61s reached the theater as the summer progressed through enemy targets that were generally sporadic. This led to several squadrons never scoring a kill for the duration of the war. In January 1945, a P-61 aided in the raid on the Cabanatuan prisoner of war camp in the Philippines by distracting the Japanese guards as the assault force neared. As the spring of 1945 progressed, Japanese targets became virtually nonexistent though a P-61 was credited with scoring the final kill of the war when it downed a Nakajima Ki-44 "Tojo" on August 14/15.

Later Service

Though concerns about the P-61's performance persisted, it was retained after the war as USAAF did not possess an effective jet-powered night fighter. The type was joined by the F-15 Reporter which had been developed during the summer of 1945. Essentially an unarmed P-61, the F-15 carried a multitude of cameras and was intended for use as a reconnaissance aircraft. Redesignated F-61 in 1948, the aircraft began to be withdrawn from service later that year and was replaced by the North American F-82 Twin Mustang. Refitted as a night fighter, the F-82 served as an interim solution until the arrival of the jet-powered F-89 Scorpion. The final F-61s were retired in May 1950. Sold to civilian agencies, F-61s and F-15s performed in a variety of roles into the late 1960s.