The major production version of the Scorpion interceptor was the F-89D (Model N-68). A total of 682 F-89D versions of the Scorpion were constructed.
The F-89D differed from the F-89C in having the armament of six 20-mm cannon replaced by an all-rocket armament. The rocket launching pods were housed in the forward edges of each of the wingtip fuel tanks. These tanks were longer and had a larger diameter than the 300-gallon tanks carried by the F-89C. The forward third of each tank contained a series of launch tubes for 52 2.75-inch Folding Fin Aircraft Rockets (FFAR). These rockets were known as Mighty Mouse, after a well-known cartoon character ("Here I come to save the day"). The outer ring of tubes had metal doors convering the rockets, while the inner honeycomb of tube were each covered with individual protective plastic caps. These rockets were unguided and had an effective range of about 2000 yards and were equipped with high-explosive warheads. The rear two thirds of the tank was taken up by 308 gallons of fuel.
With the addition of the rocket armament, the six 20-mm nose cannon were deleted. The entire nose section of the fuselage was redesigned to house a Hughes E-5 fire control system with a straight tapered nose cone and a larger and flatter radome. The E-5 fire control system consisted of a Hughes APG-40 radar and an AN/APA-84 computer. This system allowed the F-89D to make attacks and firing passes from a 90-degree "beam" position (earlier Scorpions were generally capable of only "tail-chase" interceptions). This resulted in closing speeds consistently in the range of 1,000 knots, which meant that the F-89D would be in the target aircraft's defensive cone of firepower for only a very brief time. In a typical intercept, the F-89D would pass 50 to 150 yards behind the target aircraft after firing the weapons- depending on how close the attack was made with regard to an actual 90-degree approach.
The space in the nose formerly occupied by the six cannon was used to carry an additional 262 gallon fuselage fuel tank. The F-89D could also carry extra fuel in underwing drop tanks, each containing 200 gallons, bringing total fuel capacity to 2834 gallons.
The first F-89D was obtained by modifying F-89B serial number 49-2463, the aircraft being redesignated YF-89D. It had a redesigned, longer nose housing an APG-40 radar for the Hughes E-5 fire control system. The first flight of the YF-89D took place on October 23, 1951. The first two production F-89Ds were delivered to the USAF on June 30, 1952. Some 125 F-89Ds had been built by the time that the problems with the Scorpion's wings resulted in the grounding of the entire fleet. These F-89Ds remained at the factory until the wing modifications could be made that would make the aircraft safe to operate in the field.
The first F-89Ds became operational with the 18th Fighter Interceptor Squadron based at Minneapolis/St.Paul, Minnesota on January 7, 1954.
The pilot could select several options when firing the rocket armament. The 104 rockets could all be fired at once, all the rockets leaving the tubes in only four-tenths of a second. When fired at once, the rockets could blanket an area the size of a football field, enveloping the target in a pattern reminiscent of a shotgun blast. One hit was deemed sufficient to bring down a bomber. The rockets could also be ripple fired, the pilot being able to select two ripples (82 and 42 rockets) or three ripples (42,32, and 30 rockets).
Once in service, there were some problems encountered with the F-89D which were corrected as they came up. The initial F-89Ds had the same structural deficiencies that plagued the earlier versions, which were fixed only after 170 F-89Ds had already left the production line. These planes required postproduction modifications to correct these structural defects. The first 118 F-89Ds lacked the E-5 fire control system and the E-11 autopilot of subsequent Ds. During flights at high altitude, there were mysterious drops in engine power above 30,000 feet, which were eventually traced to a temperature sensor element in the power control unit. The problem was cured by shielding the unit. In service, the rocket tubes in the wingtip pods were often subject to corrosion which, if allowed to proceed unchecked, could result in an explosion in the tube during rocket firing. A new thick-walled tube was designed which corrected this problem.
Beginning in July of 1954, F-89Ds in production were equipped with E-11 autopilots replacing the E-5
A total of 682 F-89Ds were accepted, of which 350 were modified as F-89J after delivery. The last production F-89D rolled off the line in March of 1956.
The F-89D was flown from 1954 onward by the 18th, 61st, 64th, 66th, 318th, 337th, 433rd, and 449th Fighter Interceptor Squadrons based in Alaska, as well as by the 497th Squadron. They were also flown from 1955 onward by the 11th, 58th, and 59th Fighter Interceptor Squadrons based in Labrador. The 68th, 75th, 76th , 83rd, 321st, 432nd, 437th, 445th, 460th and 465th Fighter Interceptor Squadrons received Scorpions in 1955. In 1956, Scorpions were issued to the 98th Fighter Interceptor Squadron. In 1957, the 29th, 54th, and 319th Fighter Interceptor Squadrons received Scorpions. In 1959, the 15th and 49th FIS received Scorpions.
During the peak years, 30 of the 39 Scorpion-equipped squadrons were based in the northern US or in Canada. The F-89D served in the Air Defense Command, Alaskan Air Command, and the Northeast Air command until late 1958, when they began to be replaced by supersonic types such as the F-101B Voodoo and the F-102A Delta Dagger. Ex-USAF F-89Ds were then transferred over to the ANG. The first ANG squadron to receive the F-89D was the 178th FIS of the North Dakota ANG, based at Fargo. The last Scorpions were finally withdrawn from active service with the USAF in 1961. The Air National Guard continued to fly Scorpions for several more years. The last Scorpion (an F-89J) left ANG service in 1969.
Several F-89Ds were used by Northrop to test various drones. These planes could carry two Radioplane RP-70 drones (later upgraded to RP-76 status). These drones were used as training targets for Army Nike surface-to-air missiles. The RP-76/F-89 combination was phased out in 1969.
Engines: Two Allison J33-A-33A/41/35, 5440 lb.st. dry, 7200 lb.st. with afterburner. Maximum speed: 636 mph at 10,600 feet, 523 mph at 46,500 feet. Initial climb rate 8360 feet per minute. Altitude of 46,500 feet could be attained in 18.1 minutes. Service ceiling 49,200 feet. Maximum range 1367 miles. Dimensions: wingspan 60 feet 5 inches, length 53 feet 10 inches, height 17 feet 6 inches, wing area 606 square feet. Weights 25,194 pounds empty, 37,190 pounds combat, 42,241 pounds gross, 46,789 pounds maximum takeoff. Armed with 104 2.75-inch folding fin unguided rockets in wingtip pods. Underwing racks could carry 16 five-inch rockets or 3200 pounds of bombs.
51-400/406 Northrop F-89D-1-NO Scorpion 51-407/426 Northrop F-89D-5-NO Scorpion 51-427/446 Northrop F-89D-10-NO Scorpion 51-11298/11317 Northrop F-89D-15-NO Scorpion 51-11318/11357 Northrop F-89D-20-NO Scorpion 51-11358/11407 Northrop F-89D-25-NO Scorpion 51-11408/11443 Northrop F-89D-30-NO Scorpion 52-1829/1868 Northrop F-89D-35-NO Scorpion 52-1869/1910 Northrop F-89D-40-NO Scorpion 52-1911/1961 Northrop F-89D-45-NO Scorpion 52-2127/2165 Northrop F-89D-45-NO Scorpion 53-2447/2461 Northrop F-89D-50-NO Scorpion 53-2462/2521 Northrop F-89D-55-NO Scorpion 53-2522/2581 Northrop F-89D-60-NO Scorpion 53-2582/2641 Northrop F-89D-65-NO Scorpion 53-2642/2686 Northrop F-89D-70-NO Scorpion 54-184/260 Northrop F-89D-75-NO Scorpion