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 also 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:
42-39398/39401 Northrop P-61B-1-NO Black Widow 42-39402 Northrop P-61B-2-NO Black Widow 42-39403/39405 Northrop P-61B-1-NO Black Widow 42-39406 Northrop P-61B-2-NO Black Widow 42-39407 Northrop P-61B-1-NO Black Widow 42-39408 Northrop P-61B-2-NO Black Widow 42-39409/39411 Northrop P-61B-1-NO Black Widow 42-39412/39414 Northrop P-61B-2-NO Black Widow 42-39415/39417 Northrop P-61B-1-NO Black Widow 42-39418 Northrop P-61B-2-NO Black Widow 42-39419/39423 Northrop P-61B-1-NO Black Widow 42-39424 Northrop P-61B-2-NO Black Widow 42-39425 Northrop P-61B-1-NO Black Widow 42-39426 Northrop P-61B-2-NO Black Widow 42-39427 Northrop P-61B-1-NO Black Widow 42-39428 Northrop P-61B-2-NO Black Widow 42-39429 Northrop P-61B-1-NO Black Widow 42-39430 Northrop P-61B-2-NO Black Widow 42-39431 Northrop P-61B-1-NO Black Widow 42-39432 Northrop P-61B-2-NO Black Widow 42-39433/39451 Northrop P-61B-1-NO Black Widow 42-39452/39456 Northrop P-61B-2-NO Black Widow 42-39457/39460 Northrop P-61B-1-NO Black Widow 42-39461/39462 Northrop P-61B-2-NO Black Widow 42-39463/39465 Northrop P-61B-1-NO Black Widow 42-39466 Northrop P-61B-2-NO Black Widow 42-39467/39470 Northrop P-61B-1-NO Black Widow 42-39471/39473 Northrop P-61B-2-NO Black Widow 42-39474 Northrop P-61B-1-NO Black Widow 42-39475 Northrop P-61B-2-NO Black Widow 42-39476/39477 Northrop P-61B-1-NO Black Widow 42-39478/39480 Northrop P-61B-2-NO Black Widow 42-39481/39482 Northrop P-61B-1-NO Black Widow 42-39483/39490 Northrop P-61B-2-NO Black Widow 42-39491 Northrop P-61B-1-NO Black Widow 42-39492/39493 Northrop P-61B-2-NO Black Widow 42-39494 Northrop P-61B-1-NO Black Widow 42-39495 Northrop P-61B-2-NO Black Widow 42-39496/39497 Northrop P-61B-1-NO Black Widow 42-39498/39500 Northrop P-61B-5-NO Black Widow 42-39501/39547 Northrop P-61B-6-NO Black Widow 42-39548/39572 Northrop P-61B-10-NO Black Widow 39549 and 39557 converted to XP-61E 42-39573/39611 Northrop P-61B-15-NO Black Widow 42-39612 Northrop P-61B-10-NO Black Widow 42-39613 Northrop P-61B-25-NO Black Widow 42-39614 Northrop P-61B-15-NO Black Widow 42-39615 Northrop P-61B-10-NO Black Widow 42-39616 Northrop P-61B-15-NO Black Widow 42-39617 Northrop P-61B-10-NO Black Widow 42-39618 Northrop P-61B-15-NO Black Widow 42-39619 Northrop P-61B-10-NO Black Widow 42-39620 Northrop P-61B-16-NO Black Widow 42-39621 Northrop P-61B-11-NO Black Widow 42-39622 Northrop P-61B-16-NO Black Widow 42-39623 Northrop P-61B-11-NO Black Widow 42-39624 Northrop P-61B-16-NO Black Widow 42-39625 Northrop P-61B-11-NO Black Widow 42-39626 Northrop P-61B-16-NO Black Widow 42-39627 Northrop P-61B-11-NO Black Widow 42-39628 Northrop P-61B-16-NO Black Widow 42-39629 Northrop P-61B-11-NO Black Widow 42-39630 Northrop P-61B-16-NO Black Widow 42-39631/39633 Northrop P-61B-15-NO Black Widow 42-39634/39636 Northrop P-61B-10-NO Black Widow 42-39637/39639 Northrop P-61B-15-NO Black Widow 42-39640/39641 Northrop P-61B-10-NO Black Widow 42-39642 Northrop P-61B-15-NO Black Widow 42-39643 Northrop P-61B-10-NO Black Widow 42-39644 Northrop P-61B-15-NO Black Widow 42-39645 Northrop P-61B-10-NO Black Widow 42-39646 Northrop P-61B-15-NO Black Widow 42-39647 Northrop P-61B-10-NO Black Widow 42-39648/39649 Northrop P-61B-15-NO Black Widow 42-39650 Northrop P-61B-10-NO Black Widow 42-39651 Northrop P-61B-15-NO Black Widow 42-39652 Northrop P-61B-10-NO Black Widow 42-39653 Northrop P-61B-15-NO Black Widow 42-39654 Northrop P-61B-10-NO Black Widow 42-39655 Northrop P-61B-15-NO Black Widow 42-39656 Northrop P-61B-10-NO Black Widow 42-39657 Northrop P-61B-15-NO Black Widow 42-39658 Northrop P-61B-10-NO Black Widow 42-39659/39661 Northrop P-61B-15-NO Black Widow 42-39662 Northrop P-61B-10-NO Black Widow 42-39663/39665 Northrop P-61B-15-NO Black Widow 42-39666/39667 Northrop P-61B-10-NO Black Widow 42-39668/39757 Northrop P-61B-15-NO Black Widow 43-8231/8236 Northrop P-61B-25-NO Black Widow 43-8237/8320 Northrop P-61B-20-NO Black Widow