[2] The Scorpion was designed by Northrop in response to a specification issued by the United States Army Air Forces (USAAF) during August 1945.

During March 1946, the USAAF selected both the N-24 and the rival Curtiss-Wright XP-87 Blackhawk for development, leading to an initial contract for two aircraft, designated XP-89, being approved on 13 June 1946.

Various alterations and improvements were made following a fatal accident on 22 February 1950; prior to this, officials had already specified the adoption of more powerful afterburner-equipped Allison J33-A-21 turbojet engines, AN/APG-33 radar, and the Hughes E-1 fire-control system.

During 1954, the definitive F-89D was introduced, which installed a new Hughes E-6 fire control system with AN/APG-40 radar and an AN/APA-84 computer in place of the cannon armament, being instead armed with 2.75-inch (70 mm) "Mighty Mouse" FFAR rocket pods.

The revised specification was issued on 23 November; it did not specify jet propulsion, but the desired maximum speed of 530 miles per hour (460 kn; 850 km/h) was challenging to meet via alternative means.

During March 1946, the USAAF selected the Curtiss-Wright XP-87 Blackhawk, adapted from its proposed XA-43 attack aircraft and the Northrop N-24, one of four designs submitted by the company.

[5][4] The N-24, designed by Jack Northrop, was a slim-bodied, swept-wing aircraft with a two-person, pressurized cockpit and conventional landing gear.

[8] Further changes included the position of the horizontal stabilizer also proved to be unsatisfactory, as it was affected by the engine exhaust, and it would be "blanked-out" by airflow from the wing at high angles of attack.

It was moved halfway up the tail, but its position flush with the leading edge of the vertical stabilizer proved to cause extra drag through turbulence and reduced the effectiveness of the elevators and rudder.

Another mock-up inspection was held on 17 December, and the inspectors suggested only minor changes, though the fuselage fuel tanks were still above the engines.

Northrop's efforts to protect the fuel tanks were considered sufficient, as the only alternative was redesigning the entire aircraft.

The slim rear fuselage and the high-mounted horizontal stabilizer led to Northrop employees calling it the Scorpion—a name later formally adopted by the Air Force.

[12] Pending the availability of either turret under development, an interim six-gun fixed installation, with 200 rounds per gun, was designed for the underside of the nose.

[8] On 16 August 1948, the first prototype performed its maiden flight at Muroc Army Air Field; this milestone was reached nine months later than originally scheduled.

[15][17] Several months earlier, the Air Force conducted a competitive evaluation of the three existing all-weather interceptor prototypes, the XF-87, the XF-89, and the US Navy's XF3D.

[15][19] During May 1949, the Air Force issued a cost-plus-fixed-fee contract, valued at roughly $48 million, which covered the modifications to the second prototype as well as the supply of the first 48 production standard aircraft, spare parts, tooling, ground-handling equipment, and a single static test frame.

Around this point, Air Force officials were concerned about the aircraft's poor thrust-to-weight ratio and ordered the implementation of a weight-reduction program, as well as upgrade the engines to the more powerful Allison J33-A-21 fitted with an afterburner.

[21] After repairs from a crash landing on 27 June 1949, the XF-89 was flown to March AFB to participate in the RKO movie Jet Pilot in February 1950.

Shortly afterward, the aircraft crashed on 22 February, killing the observer, when flutter developed in the elevator, and the subsequent vibrations caused the entire tail to break off.

Fixes for the problem involved the addition of a "jet wake fairing" at the bottom rear of the fuselage between the engines, external ("ice tong") mass balances for the elevator, pending the design of internal mass balances,[22] and the addition of exhaust deflectors to the fuselage to reduce the turbulence and the consequent flutter.

[25] As a result of increased unit costs, in part due to modifications, the number of production aircraft on order was reduced somewhat.

[29] The improved F-89C had started to be introduced in September 1951, although the Air Force opted to halt allocations four months later due to issues.

[39] The subsequent F-89H, which entered service in 1956, had an E-9 fire control system like that of the early F-102 and massive new wingtip pods, each holding three Falcons (usually three semi-active radar homing GAR-1s and three infrared GAR-2s) and 21 FFARs, for a total of six missiles and 42 rockets.