I really don't think it needs a radar advantage over other planes. 6400lbs of ords, and a great gun package=Drop 2 hangers and enjoy the furball afterwards.
Here is a couple blurbs about the P-61, just some interesting notes.
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The P-61 was not the most glamorous airplane of WWII. It also wasn’t the fastest, biggest, most produced, or had the highest number of kills. It did, however, have one job to do, and it did that job very well, hence the nickname “Black Widow”. It also sported a unique design, much like the P-38, which resulted in a very nice looking airplane.
The Black Widow concept began early in the war as the USAAF generals started to realize the importance of the British RADAR systems. The goal was to have a hunter/killer airplane that could fly at night and track down its prey using RADAR. Early airborne radar units were large, heavy, and power hungry. And they used antennas that looked a lot like big clunky outdoor TV antennas. As RADAR was further refined, the sets got smaller, and a version emerged that used a small parabolic dish. This would be perfect for installing in a medium twin-engined fighter aircraft. Thus was born the P-61 project.
The P-61 was a twin-boom airplane, with the engines at the front of each boom, and the tail and rudders at the back end of the booms. A pod on the centerline of the plane housed the cockpit, radar, a navigator/radar operator, and gunner. The nose of the Black Widow was fiberglass, and the radar dish sat inside the nose. The P-61 was outfitted with (2) Pratt & Whitney R-2800 Double Wasp engines, 18 cylinders each, with an output of 2000 HP per engine. Later versions of the P-61 saw that horsepower level increased to 2800 HP per engine. That increase in power boosted top speed from around 366MPH up to 440MPH. The Black Widow had a 66-foot wing span, was about 50-feet long, and sat 14-foot 8-inches tall. She weighed in at 24,000 pounds empty, and could carry an additional 16,000 pounds of payload and fuel. The offensive sting was powerful...(4) 50-caliber machine guns and (4) 20mm cannons.
The P-61 benefited from being developed later during the war. As a result, it was a very polished and refined airplane. It had a lot of automation for its day, and could literally fly itself into the air once the takeoff run was started. Pilots tell me that one could make a turn into a dead engine, something that would be suicidal in most other airplanes.
The Black Widow did not have an overwhelming number of kills in WWII. The reason is that it came along rather late in the war, and by that time, the AXIS partners had little left to throw at the Allies. If someone did dare to take to the skies under the cover of darkness, and a P-61 was nearby, they were as good as toast.
A total of 941 P-61’s were built in three models, the P-61A, P-61B, and the more powerful P-61C. In addition, 35 F-15 photo recon variants were produced. Today, only 3 survive as complete airframes, one is undergoing restoration, and one is known to survive in China
Quoted from:
http://www.visi.com/~jweeks/p61/index.html