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 actually 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 production block introduced a change in engines. These planes were 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 production block 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