The P-61A was the first production version of the Black Widow. The first P-61A-1-NO rolled off the production line in October 1943. It differed from the experimental and service-test aircraft in having a stronger framework structure for the pilot's, radar observer's and gunner's canopies. Tests with the YP-61 had uncovered the fact that the greenhouse and tail cone were so weak that they could actually implode under the pressure built up during high-speed dives. This strengthening eliminated the smooth flow of the greenhouse and created a sharper and more abrupt change in angle in that area. The welded magnesium alloy booms of the prototypes were replaced by more conventional aluminum alloy booms, since they were less expensive and easier to manufacture. Unlike the earlier XP-61 and YP-61 aircraft which were painted flat black, the P-61A was painted standard Army olive drab overall.

Only the first thirty-seven of the 45 P-61A-1s were actually equipped with the dorsal turrets. In fact, more than half of all P-61As built had this turret deleted. One reason for this omission was that the General Electric remotely-controlled turret mechanism was urgently needed for the B-29 program. However, the primary reason was the occurrence of severe aerodynamic buffeting when the turret was being either elevated or rotated in azimuth during flight. Many flight-test hours were spent in trying to solve this problem, but it was never completely eliminated. In fact, this problem was often so severe that many P-61As in the field had the four 0.50-inch machine guns in the top turret permanently locked into the forward-firing position, being fired only by the pilot, with the gunner having no control at all. In many cases, the top turret was completely removed from the aircraft, and the cavity left behind by the deletion of the gun turret was filled up by an extra fuel tank and was faired over. In a few cases, the turret mechanism was completely removed from the aircraft and the four dorsal machine guns were secured in the upper portion of the turret cavity and covered by a nonstandard turret cover. Some of these modifications were made in the field, but others were made at forward depots before the aircraft were delivered to their operational squadrons. 

Since the gunner of these re-equipped Black Widows now had no guns that he could fire, he was sometimes left at home when these planes went out on operational missions, and many Black Widow operational missions carried only two crew members--the pilot and the radar operator. However, on other occasions, the gunner was nevertheless included on operational missions, if only to act as another pair of eyes.

Most of the P-61A-1-NOs went to the USAAF night fighter squadrons in the Pacific. The 6th Night Fighter Squadron was the first to receive the new fighter.

The P-61 was quite docile despite its size. Full control of the aircraft could be maintained with one engine out, even when fully loaded. The plane could be slow-rolled into a dead engine, a maneuver which would ordinarily have been suicidal.

P-61A-1-NO 42-5496 was supplied to the RAF for tests. It was in British hands between March 21, 1944 and February 22, 1945. The RAF was not too enthusiastic about its performance, and never bothered to order any Black Widows for its own use, finding that the night fighter version of the de Havilland Mosquito was more than adequate for the task at hand.

The P-61A-5-NO introduced a change in engines. It was powered by a pair of 2250 hp R-2800-65 engines, replacing the 2000 hp R-2800-10s. Maximum speed was 322 mph at sea level, 355 mph at 10,000 feet, and 369 mph at 20,000 feet. Range (clean) was 415 miles at 319 mph at 20,000 feet and 1010 miles at 224 mph at 10,000 feet. Range with maximum external fuel was 1900 miles at 221 mph at 10,000 feet. An altitude of 5000 feet could be reached in 2.2 minutes, and 15,000 feet in 7.6 minutes. Service ceiling was 33,100 feet. Weights were 20,965 pounds empty, 27,600 pounds normal loaded, and 32,400 pounds maximum. Dimensions were wingspan 66 feet 0 inches, length 48 feet 11 inches, height 14 feet 2 inches, and wing area 664 square feet.

The P-61A-10-NO had a pair of water-injected R-2800-65 Double Wasps. This model was the first to carry the shiny-black paint job which was to be the trademark of the Black Widow. Previous production P-61As had conventional olive-drab paint jobs. 120 P-61A-10-NOs were built. 20 of these were modified prior to delivery by the addition of a pylon on the outer wing panels to carry either a pair of 265 gallon fuel tanks (later 310 gallon tanks were fitted) or a pair of 1600-pound bombs. These planes were redesignated P-61A-11.

Serials of the P-61As were as follows:
42-5485/5529 Northrop P-61A-1-NO Black Widow
42-5530/5564 Northrop P-61A-5-NO Black Widow
5559 was modified as XP-61D
42-5565/5604 Northrop P-61A-10-NO Black Widow
5587 was modified as XP-61D
42-5605/5606 Northrop P-61A-11-NO Black Widow
42-5607 Northrop P-61A-10-NO Black Widow
42-5608/5614 Northrop P-61A-11-NO Black Widow
42-5615/5634 Northrop P-61A-10-NO Black Widow
42-39348/39374 Northrop P-61A-10-NO Black Widow
42-39375/39384 Northrop P-61A-11-NO Black Widow
42-39385/39386 Northrop P-61A-10-NO Black Widow
42-39387 Northrop P-61A-11-NO Black Widow
42-39388/39397 Northrop P-61A-10-NO Black Widow

 

P-61A Plan View

Another Plan View

The P-61B was the next production version of the Black Widow. It was basically similar to the P-61A version, but introduced numerous improvements and refinements that were suggested by operational experience in the field. The P-61B version of the Black Widow introduced the improved SCR-720C A/I radar. The P-61B had an eight-inch longer crew nacelle. The A-model's hydraulically-operated main landing-gear doors which had experienced reliability problems in the field were replaced by mechanically-operated doors. The P-61B introduced split main landing gear doors. The split main-gear doors allowed the aft three-quarters of the doors to close back down again after the gear had been extended, preventing mud, rocks and other debris from being thrown up into the wheelwells during takeoffs or landings. A main landing gear down-lock emergency release was introduced, which allowed the pilot to release the locks in an emergency even if the entire hydraulic system malfunctioned. A safety latch was added to the main gear hydraulic valve handle to eliminate the possibility of the pilot inadvertently retracting the gear while the plane was on the ground. One way of visually telling the difference between a P-61A and a P-61B was by an readily-noticeable access panel which was added behind the radome on the P-61B.

The B-model had a bigger and better heater system for the crew, and it had automatically- operated lower engine cowl flops, oil-cooler air exit flaps, and intercooler flaps. The oil tanks were mounted inside the engine nacelles instead of inside the outer wings. A taxi lamp was added to the landing gear strut. The aileron trim tabs were deleted, and a built-in fire extinguisher system was added.

Operational crews in combat theatres as well as training squadrons in the USA determined very early on that the Black Widow pilot needed to have night-vision binoculars in order to see his target. These were introduced on the B-model. Night-vision binoculars consisted of a combination of 5.8-power night glasses and an optical gunsight. In place of the circle and the dot of light in his regular gunsight, there was a horizontal row of four illuminated dots in the gunsight of the binoculars. The pilot lined up these dots with the wing of the target aircraft he was sighting on, and if he knew the type of aircraft he was looking at, he could easily determine its range and quickly calculate a firing solution. Night binoculars were later retrofitted to many P-61A already in the field. Starting with the P-51B-5-NO production block, the SCR-718 radio altimeter was replaced with an APN-1 low-altitude altimeter. Starting with the P-61B-10-NO block, an APS-13 tail-warning system was added. Some P-61As and many early P-61Bs were retrofitted in the field with the APN-1 and APS-13 systems. The B-10 production block also introduced underwing pylons for four 258-gallon drop tanks or four 1600-pound bombs

The P-61B-15-NO reintroduced the dorsal turret (General Electric Type A-4), the buffeting problem caused by earlier turrets having by now been largely corrected.

The P-61B-20-NO used the General Electric Type A-7 turret with a revised fire-control system.

The Black Widow night fighter used its on-board radar only to plot intercept courses when pursuing enemy aircraft. Once having used closed with his target, the pilot of the Black Widow sighted his prey by eye and used a conventional optical gunsight to fire his guns at the enemy. Operationally-practical radar-directed airborne fire control was still many years in the future. Nevertheless, there were some experiments with the Black Widow in which automatic airborne fire control was tried out.

The P-61B-25-NO was a block of seven experimental aircraft which were fitted with a Western Electric APG-1 gun-laying radar which was coupled with a General Electric remote-controlled turret system. The radar fed data into an analogue computer, which in turn directed the turret guns onto the target.

One P-61B-15-NO was also modified in this fashion, and the first six P-61B-20-NO aircraft were also modified to this configuration. All of these aircraft were tested by the Air Proving Command at Elgin Field, Florida and at the night fighter training establishment at Hammer Field in California. However, I don't think that this innovation ever made it to the field. During 1945, 16 P-61Bs were converted to P-61Gs for weather reconnaissance. All armament was deleted.

Serials of the P-61B were as follows

 

P-61B Plan View

Another Plan view of the P-61 B

 

 

Another plan view. Note that the P-61 A-11, B-2, B-6, B-11 and B-16 carried wing fuel tanks outside the engines. Inner and outer tanks were on the P-61 B-10 only.

 

Nose Wheel
The P-61 A and B nose section. Note the 8-inch insert on the B model

 

Turret

Trim Tabs

Main Gear

 
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